added @thunder

a tone generator.

.gitignore

@@ -42,3 +42,4 @@
 .pio/*
 members/*/.pio/
 members/*/.pio/*
+.python-version

0-set-group.list

@@ -0,0 +1,172 @@
+==== ADDRESSBOOK ====
+
+1- my id: 20001, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:0A:07, channel: 5
+2- my id: 20002, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: EC:FA:BC:63:19:84, channel: 5
+3- my id: 20003, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 98:F4:AB:B3:B4:19, channel: 5
+4- my id: 20004, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 98:F4:AB:B3:B4:DD, channel: 5
+5- my id: 20005, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: BC:DD:C2:14:74:D2, channel: 5
+6- my id: 20006, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: BC:DD:C2:14:75:6F, channel: 5
+7- my id: 20007, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:45:F5, channel: 5
+8- my id: 20008, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 84:CC:A8:A3:A7:B5, channel: 5
+9- my id: 20009, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:11:E6, channel: 5
+a- my id: 20010, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: BC:DD:C2:14:63:8E, channel: 5
+b- my id: 20011, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 98:F4:AB:B3:BA:44, channel: 5
+c- my id: 20012, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 5C:CF:7F:B8:B6:80, channel: 5
+d- my id: 20013, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:18:AE, channel: 5
+e- my id: 20014, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 98:F4:AB:B3:B5:C2, channel: 5
+f- my id: 20015, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:37:AE, channel: 5
+g- my id: 20016, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: BC:DD:C2:B2:AF:D4, channel: 5
+h- my id: 20017, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 68:C6:3A:D5:3E:F3, channel: 5
+i- my id: 20018, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: B4:E6:2D:37:09:92, channel: 5
+j- my id: 20019, gid: 20000, call me ==> "@POSTMAN|@SAMPLER"- mac address: 5C:CF:7F:B7:55:98, channel: 5
+
+repeaters
+10- my id: 21010, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: A8:48:FA:CD:29:76, channel: 5
+11- my id: 21011, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 30:83:98:B1:D2:66, channel: 5
+12- my id: 21012, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 30:83:98:B2:77:E6, channel: 5
+13- my id: 21013, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 30:83:98:B2:6C:7B, channel: 5
+14- my id: 21014, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 60:01:94:38:20:5B, channel: 5
+15- my id: 21015, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: A8:48:FA:CD:47:84, channel: 5
+16- my id: 21016, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: A8:48:FA:CD:43:A7, channel: 5
+17- my id: 21017, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: B4:E6:2D:37:3B:90, channel: 5
+18- my id: 21018, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: A8:48:FA:CD:1C:53, channel: 5
+19- my id: 21019, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 80:7D:3A:58:87:2D, channel: 5
+20- my id: 21020, gid: 20000, call me ==> "@POSTMAN|REPEATER"- mac address: 30:83:98:B1:18:B4, channel: 5
+
+
+==== GROUPS ====
+[slopeway]        => 5 11 8 12 a    + c 2 13 4 i j e f 19 7 6
+5  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:74:D2
+11 : "@POSTMAN|REPEATER" => 30:83:98:B1:D2:66
+8  : "@POSTMAN|@SAMPLER" => 84:CC:A8:A3:A7:B5
+12 : "@POSTMAN|REPEATER" => 30:83:98:B2:77:E6
+a  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:63:8E
++
+c  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B8:B6:80
+2  : "@POSTMAN|@SAMPLER" => EC:FA:BC:63:19:84
+13 : "@POSTMAN|REPEATER" => 30:83:98:B2:6C:7B
+4  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B4:DD
+i  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:09:92
+j  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B7:55:98
+e  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B5:C2
+f  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:37:AE
+19 : "@POSTMAN|REPEATER" => 80:7D:3A:58:87:2D
+7  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:45:F5
+6  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:75:6F
++
+broadcast
+----------------
+[1st floor]       => c 2 10 b 14 3  + slopeway(5 11 8 12 a)
+c  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B8:B6:80
+2  : "@POSTMAN|@SAMPLER" => EC:FA:BC:63:19:84
+10 : "@POSTMAN|REPEATER" => A8:48:FA:CD:29:76
+b  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:BA:44
+14 : "@POSTMAN|REPEATER" => 60:01:94:38:20:5B
+3  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B4:19
++
+5  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:74:D2
+11 : "@POSTMAN|REPEATER" => 30:83:98:B1:D2:66
+8  : "@POSTMAN|@SAMPLER" => 84:CC:A8:A3:A7:B5
+12 : "@POSTMAN|REPEATER" => 30:83:98:B2:77:E6
+a  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:63:8E
++
+broadcast
+----------------
+[2nd floor]       => 4 j i 13 e f h + slopeway(5 11 8 12 a) + bridge(15 16 1 17)
+4  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B4:DD
+j  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B7:55:98
+i  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:09:92
+13 : "@POSTMAN|REPEATER" => 30:83:98:B2:6C:7B
+e  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B5:C2
+f  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:37:AE
+h  : "@POSTMAN|@SAMPLER" => 68:C6:3A:D5:3E:F3
++
+5  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:74:D2
+11 : "@POSTMAN|REPEATER" => 30:83:98:B1:D2:66
+8  : "@POSTMAN|@SAMPLER" => 84:CC:A8:A3:A7:B5
+12 : "@POSTMAN|REPEATER" => 30:83:98:B2:77:E6
+a  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:63:8E
++
+15 : "@POSTMAN|REPEATER" => A8:48:FA:CD:47:84
+16 : "@POSTMAN|REPEATER" => A8:48:FA:CD:43:A7
+1  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:0A:07
+17 : "@POSTMAN|REPEATER" => B4:E6:2D:37:3B:90
++
+broadcast
+----------------
+[bridge]          => 15 16 1 17     + h 13 18 9
+15 : "@POSTMAN|REPEATER" => A8:48:FA:CD:47:84
+16 : "@POSTMAN|REPEATER" => A8:48:FA:CD:43:A7
+1  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:0A:07
+17 : "@POSTMAN|REPEATER" => B4:E6:2D:37:3B:90
++
+h  : "@POSTMAN|@SAMPLER" => 68:C6:3A:D5:3E:F3
+13 : "@POSTMAN|REPEATER" => 30:83:98:B2:6C:7B
+18 : "@POSTMAN|REPEATER" => A8:48:FA:CD:1C:53
+9  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:11:E6
++
+broadcast
+----------------
+[2nd floor annex] => 18 g 9         + bridge(15 16 1 17)
+18 : "@POSTMAN|REPEATER" => A8:48:FA:CD:1C:53
+g  : "@POSTMAN|@SAMPLER" => BC:DD:C2:B2:AF:D4
+9  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:11:E6
++
+15 : "@POSTMAN|REPEATER" => A8:48:FA:CD:47:84
+16 : "@POSTMAN|REPEATER" => A8:48:FA:CD:43:A7
+1  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:0A:07
+17 : "@POSTMAN|REPEATER" => B4:E6:2D:37:3B:90
++
+broadcast
+----------------
+[3rd floor]       => 7 19 20 6 d    + slopeway(5 11 8 12 a)
+7  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:45:F5
+19 : "@POSTMAN|REPEATER" => 80:7D:3A:58:87:2D
+20 : "@POSTMAN|REPEATER" => 30:83:98:B1:18:B4
+6  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:75:6F
+d  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:18:AE
++
+5  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:74:D2
+11 : "@POSTMAN|REPEATER" => 30:83:98:B1:D2:66
+8  : "@POSTMAN|@SAMPLER" => 84:CC:A8:A3:A7:B5
+12 : "@POSTMAN|REPEATER" => 30:83:98:B2:77:E6
+a  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:63:8E
+----------------
+
+
+
+
+
+
+1  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:0A:07 [bridge]
+2  : "@POSTMAN|@SAMPLER" => EC:FA:BC:63:19:84 [1st floor]
+3  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B4:19 [1st floor]
+4  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B4:DD [2nd floor]
+5  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:74:D2 [slopeway]
+6  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:75:6F [3rd floor]
+7  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:45:F5 [3rd floor]
+8  : "@POSTMAN|@SAMPLER" => 84:CC:A8:A3:A7:B5 [slopeway]
+9  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:11:E6 [2nd floor annex]
+a  : "@POSTMAN|@SAMPLER" => BC:DD:C2:14:63:8E [slopeway]
+b  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:BA:44 [1st floor]
+c  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B8:B6:80 [1st floor]
+d  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:18:AE [3rd floor]
+e  : "@POSTMAN|@SAMPLER" => 98:F4:AB:B3:B5:C2 [2nd floor]
+f  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:37:AE [2nd floor]
+g  : "@POSTMAN|@SAMPLER" => BC:DD:C2:B2:AF:D4 [2nd floor annex]
+h  : "@POSTMAN|@SAMPLER" => 68:C6:3A:D5:3E:F3 [2nd floor]
+i  : "@POSTMAN|@SAMPLER" => B4:E6:2D:37:09:92 [2nd floor]
+j  : "@POSTMAN|@SAMPLER" => 5C:CF:7F:B7:55:98 [2nd floor]
+
+
+10 : "@POSTMAN|REPEATER" => A8:48:FA:CD:29:76 [1st floor]
+11 : "@POSTMAN|REPEATER" => 30:83:98:B1:D2:66 [slopeway]
+12 : "@POSTMAN|REPEATER" => 30:83:98:B2:77:E6 [slopeway]
+13 : "@POSTMAN|REPEATER" => 30:83:98:B2:6C:7B [2nd floor]
+14 : "@POSTMAN|REPEATER" => 60:01:94:38:20:5B [1st floor]
+15 : "@POSTMAN|REPEATER" => A8:48:FA:CD:47:84 [bridge]
+16 : "@POSTMAN|REPEATER" => A8:48:FA:CD:43:A7 [bridge]
+17 : "@POSTMAN|REPEATER" => B4:E6:2D:37:3B:90 [bridge]
+18 : "@POSTMAN|REPEATER" => A8:48:FA:CD:1C:53 [2nd floor annex]
+19 : "@POSTMAN|REPEATER" => 80:7D:3A:58:87:2D [3rd floor]
+20 : "@POSTMAN|REPEATER" => 30:83:98:B1:18:B4 [3rd floor]

@bell/platformio.ini

@@ -0,0 +1,45 @@
+; < NOTE >
+
+; to enable verbose output add option -->
+; $ platformio run --verbose
+
+; to make this permanent for the proj. -->
+; $ platformio settings set force_verbose Yes
+
+; then confirm the change -->
+; $ platformio settings get
+
+
+; // pio v 4.0 'Build options'
+;    - build_type
+;    - build_flags
+;    - src_build_flags
+;    - build_unflags
+;    - src_filter
+;    - targets
+
+
+[platformio]
+default_envs = nodemcuv2
+
+[env]
+framework = arduino
+upload_port =
+  /dev/ttyUSB0
+  /dev/tty.SLAB_USBtoUART
+lib_deps =
+  721 ; TaskScheduler
+
+[env:nodemcuv2]
+platform = espressif8266
+board = nodemcuv2
+lib_deps =
+  ${env.lib_deps}
+upload_speed = 921600 ; 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600
+
+[env:d1_mini_pro]
+platform = espressif8266
+board = d1_mini_pro
+lib_deps =
+  ${env.lib_deps}
+upload_speed = 460800 ; 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600

@bell/src/main.cpp

@@ -0,0 +1,524 @@
+//
+// wirelessly connected cloud (based on ESP-NOW, a kind of LPWAN?)
+//
+
+//
+// `hing @ dianaband studio, Seoul
+//
+
+//
+// 2021 02 15
+//
+//   this module will be an esp-now node in a group.
+//       like, a bird in a group of birds.
+//
+//   esp-now @ esp8266 w/ broadcast address (FF:FF:FF:FF:FF:FF)
+//       always broadcasting. everyone is 'talkative'.
+//
+
+// then, let it save a value in EEPROM (object with memory=mind?)
+
+//============<identities>============
+//
+#define MY_GROUP_ID       (11000)
+#define MY_ID             (MY_GROUP_ID + 1)
+#define MY_SIGN           ("BELL")
+#define ADDRESSBOOK_TITLE ("broadcast only")
+//
+//============</identities>============
+
+//==========<list-of-configurations>===========
+//
+// 'HAVE_CLIENT'
+// --> i have a client. enable the client task.
+//
+// 'SERIAL_SWAP'
+// --> UART pin swapped.
+//     you want this, when you want a bi-directional comm. to external client boards (e.g. teensy).
+//
+// 'DISABLE_AP'
+// --> (questioning)...
+//
+// 'REPLICATE_NOTE_REQ' (+ N_SEC_BLOCKING_NOTE_REQ)
+// --> for supporting wider area with simple esp_now protocol,
+//     all receipents will replicate NOTE msg. when they are newly appeared.
+//   + then, network would be flooded by infinite duplicating msg.,
+//     unless they stop reacting to 'known' req. for some seconds. (e.g. 3 seconds)
+
+// 'HAVE_CLIENT_I2C'
+// --> i have a client w/ I2C i/f. enable the I2C client task.
+//
+// 'ADDRESSBOOK_TITLE'
+// --> peer list limited max. 20.
+//     so, we might use different address books for each node to cover a network of more than 20 nodes.
+//
+//==========</list-of-configurations>==========
+//
+// (EMPTY)
+#define DISABLE_AP
+// #define REPLICATE_NOTE_REQ
+
+//============<bell>============
+#define BELL_HIT_KEY 105
+//============</bell>===========
+
+//============<parameters>============
+//
+#define LED_PERIOD (11111)
+#define LED_ONTIME (1)
+#define LED_GAPTIME (222)
+//
+#define WIFI_CHANNEL 1
+//
+// 'MONITORING_SERIAL'
+//
+// --> sometimes, the 'Serial' is in use (for example, 'osc' node)
+//     then,      use 'Serial1' - D4/GPIO2/TDX1 @ nodemcu (this is TX only.)
+//
+// --> otherwise, MONITORING_SERIAL == Serial.
+//
+#if defined(SERIAL_SWAP)
+#define MONITORING_SERIAL (Serial1)
+#else
+#define MONITORING_SERIAL (Serial)
+#endif
+//
+//============</parameters>===========
+
+//============<board-specifics>============
+#if defined(ARDUINO_FEATHER_ESP32) // featheresp32
+#define LED_PIN 13
+#else
+#define LED_PIN 2
+#endif
+//============</board-specifics>===========
+
+//arduino
+#include <Arduino.h>
+
+//post & addresses
+#include "../../post.h"
+
+//vector
+#include <vector>
+std::vector<Note> recentNotes;
+
+//espnow
+#include <ESP8266WiFi.h>
+#include <espnow.h>
+AddressLibrary lib;
+
+//task
+#include <TaskScheduler.h>
+Scheduler runner;
+
+//
+#if defined(REPLICATE_NOTE_REQ)
+Note note_now = {
+  -1, // int32_t id;
+  -1, // float pitch;
+  -1, // float velocity;
+  -1, // float onoff;
+  -1, // float x1;
+  -1, // float x2;
+  -1, // float x3;
+  -1, // float x4;
+  -1 // float ps;
+};
+#define RECENT_NOTES_TIMEOUT (3000)
+static unsigned long last_note_time = 0;
+void recent_clear() {
+  //
+  if (millis() - last_note_time > RECENT_NOTES_TIMEOUT) {
+    recentNotes.clear();
+    Serial.println("recent list cleared");
+    last_note_time = millis();
+  }
+  //
+}
+Task recent_clear_task(100, TASK_FOREVER, &recent_clear, &runner, true);
+#endif
+//-*-*-*-*-*-*-*-*-*-*-*-*-
+// servo
+#include <Servo.h>
+
+#define SERVO_PIN D6
+Servo myservo;
+int hitting_angle = 90;
+int release_angle = 60;
+int stabilize_angle = 53;
+
+//
+extern Task hit_task;
+
+//
+extern Task pcontrol_task;
+bool pcontrol_new = false;
+int pcontrol_start = 0;
+int pcontrol_target = 0;
+int control_count = 0;
+
+//
+extern Task servo_release_task;
+
+// my tasks
+// hit!
+void hit() {
+  static int count = 0;
+  if (hit_task.isFirstIteration()) {
+    count = 0;
+    Serial.println("hit! start.");
+  }
+  if (count % 3 == 0) {
+    //
+    myservo.attach(SERVO_PIN);
+    myservo.write(release_angle);
+    // servo_release_task.restartDelayed(200);
+    //
+  } else if (count % 3 == 1) {
+    //
+    myservo.attach(SERVO_PIN);
+    myservo.write(hitting_angle);
+    // servo_release_task.restartDelayed(200);
+    //
+    Serial.print("bell, bell, bell! : ");
+    Serial.print(hitting_angle);
+    Serial.println(" deg.");
+    //
+  } else {
+    //
+    myservo.attach(SERVO_PIN);
+    myservo.write(release_angle);
+    servo_release_task.restartDelayed(200);
+    //
+    Serial.print("release to .. : ");
+    Serial.print(release_angle);
+    Serial.println(" deg.");
+    // start stablizing..
+    pcontrol_new = true;
+    pcontrol_start = release_angle;
+    pcontrol_target = stabilize_angle;
+    pcontrol_task.restartDelayed(80);
+    //
+    control_count = 0;
+  }
+  //
+  count++;
+}
+Task hit_task(100, 3, &hit);
+
+// pcontrol
+void pcontrol() {
+  static int angle;
+  if (pcontrol_new == true) {
+    pcontrol_new = false;
+    angle = pcontrol_start;
+  }
+  int error = pcontrol_target - angle;
+  int sign = (error >= 0 ? 1 : -1);
+  //
+  Serial.print("step-by-step to.. : ");
+  Serial.println(sign);
+  //
+  if (error != 0) {
+    angle = angle + sign; // most gentle move : 1 step each time.
+    //
+    Serial.print("stablizing in action ==> next angle : ");
+    Serial.print(angle);
+    Serial.println(" deg.");
+    //
+    myservo.attach(SERVO_PIN);
+    myservo.write(angle);
+    servo_release_task.restartDelayed(50);
+    pcontrol_task.restartDelayed(400);
+  }
+  else {
+    // stand-by processes
+    if (control_count % 2 == 0) {
+      pcontrol_new = true;
+      pcontrol_start = stabilize_angle;
+      pcontrol_target = release_angle;
+      pcontrol_task.restartDelayed(300);
+    } else if (control_count % 2 == 1) {
+      pcontrol_new = true;
+      pcontrol_start = release_angle;
+      pcontrol_target = stabilize_angle;
+      pcontrol_task.restartDelayed(300);
+    }
+    //
+    control_count++;
+  }
+}
+Task pcontrol_task(0, TASK_ONCE, &pcontrol); // hit -> 100ms -> step back -> 50ms -> slowly move to rest pos.
+
+// pcontrol release
+void servo_release() {
+  myservo.detach();
+}
+Task servo_release_task(0, TASK_ONCE, &servo_release);
+//*-*-*-*-*-*-*-*-*-*-*-*-*
+
+//
+extern Task hello_task;
+static int hello_delay = 0;
+void hello() {
+  //
+  byte mac[6];
+  WiFi.macAddress(mac);
+  uint32_t mac32 = (((((mac[2] << 8) + mac[3]) << 8) + mac[4]) << 8) + mac[5];
+  //
+  Hello hello(String(MY_SIGN), MY_ID, mac32); // the most basic 'hello'
+  // and you can append some floats
+  static int count = 0;
+  count++;
+  hello.h1 = (count % 1000);
+  // hello.h2 = 0;
+  // hello.h3 = 0;
+  // hello.h4 = 0;
+  //
+  uint8_t frm_size = sizeof(Hello) + 2;
+  uint8_t frm[frm_size];
+  frm[0] = '{';
+  memcpy(frm + 1, (uint8_t *) &hello, sizeof(Hello));
+  frm[frm_size - 1] = '}';
+  //
+  esp_now_send(NULL, frm, frm_size); // to all peers in the list.
+  //
+  // MONITORING_SERIAL.write(frm, frm_size);
+  // MONITORING_SERIAL.println(" ==(esp_now_send/0)==> ");
+  //
+  if (hello_delay > 0) {
+    if (hello_delay < 100) hello_delay = 100;
+    hello_task.restartDelayed(hello_delay);
+  }
+}
+Task hello_task(0, TASK_ONCE, &hello, &runner, false);
+
+//task #0 : blink led
+extern Task blink_task;
+void blink() {
+  //
+  static int count = 0;
+  count++;
+  //
+  switch (count % 4) {
+  case 0:
+    digitalWrite(LED_PIN, LOW); // first ON
+    blink_task.delay(LED_ONTIME);
+    break;
+  case 1:
+    digitalWrite(LED_PIN, HIGH); // first OFF
+    blink_task.delay(LED_GAPTIME);
+    break;
+  case 2:
+    digitalWrite(LED_PIN, LOW); // second ON
+    blink_task.delay(LED_ONTIME);
+    break;
+  case 3:
+    digitalWrite(LED_PIN, HIGH); // second OFF
+    blink_task.delay(LED_PERIOD - 2* LED_ONTIME - LED_GAPTIME);
+    break;
+  }
+}
+Task blink_task(0, TASK_FOREVER, &blink, &runner, true); // -> ENABLED, at start-up.
+
+// on 'Note'
+void onNoteHandler(Note & n) {
+  //is it for me?
+  if (n.id == MY_GROUP_ID || n.id == MY_ID) {
+    //
+    if (n.pitch == BELL_HIT_KEY) {
+      if (n.onoff == 1) {
+        hitting_angle = n.velocity;
+        release_angle = n.x1;
+        stabilize_angle = n.x2;
+        hit_task.restartDelayed(10);
+      }
+    }
+  }
+}
+
+// on 'receive'
+void onDataReceive(uint8_t * mac, uint8_t *incomingData, uint8_t len) {
+
+  //
+  //MONITORING_SERIAL.write(incomingData, len);
+
+  //
+#if defined(HAVE_CLIENT)
+  Serial.write(incomingData, len); // we pass it over to the client.
+#endif
+
+  // open => identify => use.
+  if (incomingData[0] == '{' && incomingData[len - 1] == '}' && len == (sizeof(Hello) + 2)) {
+    Hello hello("");
+    memcpy((uint8_t *) &hello, incomingData + 1, sizeof(Hello));
+    //
+    MONITORING_SERIAL.println(hello.to_string());
+    //
+  }
+
+  // open => identify => use.
+  if (incomingData[0] == '[' && incomingData[len - 1] == ']' && len == (sizeof(Note) + 2)) {
+    Note note;
+    memcpy((uint8_t *) &note, incomingData + 1, sizeof(Note));
+    onNoteHandler(note);
+
+    //is it for me?
+    if (note.id == MY_GROUP_ID || note.id == MY_ID) {
+      hello_delay = note.ps;
+      if (hello_delay > 0 && hello_task.isEnabled() == false) {
+        hello_task.restart();
+      }
+    }
+
+    MONITORING_SERIAL.println(note.to_string());
+
+    #if defined(REPLICATE_NOTE_REQ)
+    last_note_time = millis(); //clear timer reset : the recent list holding (re)started
+    // check if this note is in the list?
+    bool check = false;
+    for (uint32_t idx = 0; idx < recentNotes.size(); idx++) {
+      if (recentNotes[idx].pitch == note.pitch && recentNotes[idx].id == note.id) {
+        check = true;
+      }
+    }
+    // if not, add this into the list and repeat!
+    if (check == false) {
+      //
+      recentNotes.push_back(note);
+      //
+      uint8_t frm_size = sizeof(Note) + 2;
+      uint8_t frm[frm_size];
+      frm[0] = '[';
+      memcpy(frm + 1, (uint8_t *) &note, sizeof(Note));
+      frm[frm_size - 1] = ']';
+      //
+      esp_now_send(NULL, frm, frm_size); // to all peers in the list.
+      //
+      MONITORING_SERIAL.print("repeat! ==> ");
+      MONITORING_SERIAL.println(note.to_string());
+      //
+    }
+
+    //EMERGENCY PATCH.HACK:
+    // original code is not intended for a BURST of notes.
+    // so, only 1 msg. will be repeated in 3 sec. all others will be simply ignored.
+    // to make a burst of msgs repeatible:
+    // --> make a list of recent 'pitches'
+    //     if there is any new msg. check if this is in the list, if not, add it & repeat, if yes, skip it.
+    //     after 3sec no new msg., the list will be flushed. every new msg. will reset timeout + save the list for extra. 3 sec.
+    #endif
+  }
+}
+
+// on 'sent'
+void onDataSent(uint8_t *mac_addr, uint8_t sendStatus) {
+  char buff[256] = "";
+  sprintf(buff, "Delivery failed! -> %02X:%02X:%02X:%02X:%02X:%02X",  mac_addr[0],  mac_addr[1],  mac_addr[2],  mac_addr[3],  mac_addr[4],  mac_addr[5]);
+  if (sendStatus != 0) MONITORING_SERIAL.println(buff);
+}
+
+//
+void setup() {
+
+  //led
+  pinMode(LED_PIN, OUTPUT);
+
+  //serial
+  Serial.begin(115200);
+  delay(100);
+
+  //info
+  Serial.println();
+  Serial.println();
+  Serial.println("\"hi, i m your postman.\"");
+  Serial.println("-");
+  Serial.println("- my id: " + String(MY_ID) + ", gid: " + String(MY_GROUP_ID) + ", call me ==> \"" + String(MY_SIGN) + "\"");
+  Serial.println("- mac address: " + WiFi.macAddress() + ", channel: " + String(WIFI_CHANNEL));
+#if defined(HAVE_CLIENT)
+  Serial.println("- ======== 'HAVE_CLIENT' ========");
+#endif
+#if defined(SERIAL_SWAP)
+  Serial.println("- ======== 'SERIAL_SWAP' ========");
+#endif
+#if defined(DISABLE_AP)
+  Serial.println("- ======== 'DISABLE_AP' ========");
+#endif
+#if defined(HAVE_CLIENT_I2C)
+  Serial.println("- ======== 'HAVE_CLIENT_I2C' ========");
+#endif
+#if defined(REPLICATE_NOTE_REQ)
+  Serial.println("- ======== 'REPLICATE_NOTE_REQ' ========");
+#endif
+  Serial.println("-");
+
+  //wifi
+  WiFiMode_t node_type = WIFI_AP_STA;
+#if defined(DISABLE_AP)
+  system_phy_set_max_tpw(0);
+  node_type = WIFI_STA;
+#endif
+  WiFi.mode(node_type);
+
+  //esp-now
+  if (esp_now_init() != 0) {
+    Serial.println("Error initializing ESP-NOW");
+    return;
+  }
+  esp_now_set_self_role(ESP_NOW_ROLE_COMBO);
+  esp_now_register_send_cb(onDataSent);
+  esp_now_register_recv_cb(onDataReceive);
+  //
+  // Serial.println("- ! (esp_now_add_peer) ==> add a 'broadcast peer' (FF:FF:FF:FF:FF:FF).");
+  // uint8_t broadcastmac[6] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
+  // esp_now_add_peer(broadcastmac, ESP_NOW_ROLE_COMBO, 1, NULL, 0);
+
+  AddressBook * book = lib.getBookByTitle(ADDRESSBOOK_TITLE);
+  if (book == NULL) {
+    Serial.println("- ! wrong book !! : \"" + String(ADDRESSBOOK_TITLE) + "\""); while(1);
+  }
+  for (int idx = 0; idx < book->list.size(); idx++) {
+    Serial.println("- ! (esp_now_add_peer) ==> add a '" + book->list[idx].name + "'.");
+#if defined(ESP32)
+    esp_now_peer_info_t peerInfo = {};
+    memcpy(peerInfo.peer_addr, book->list[idx].mac, 6);
+    peerInfo.channel = 0;
+    peerInfo.encrypt = false;
+    esp_now_add_peer(&peerInfo);
+#else
+    esp_now_add_peer(book->list[idx].mac, ESP_NOW_ROLE_COMBO, 1, NULL, 0);
+#endif
+  }
+  // (DEBUG) fetch full peer list
+  { PeerLister a; a.print(); }
+  //
+  Serial.println("-");
+  Serial.println("\".-.-.-. :)\"");
+  Serial.println();
+
+#if defined(SERIAL_SWAP)
+  Serial.println("-      ======== 'SERIAL_SWAP' ========");
+  // a proper say goodbye.
+  Serial.println("\"bye, i will do 'swap' in 1 second. find me on alternative pins!\"");
+  Serial.println("\"    hint: osc wiring ==> esp8266(serial.swap) <-> teensy(serial3)\"");
+  Serial.println("-");
+  Serial.println("\".-.-.-. :)\"");
+  delay(1000);   // flush out unsent serial messages.
+
+  // moving...
+  Serial.swap(); // use RXD2/TXD2 pins, afterwards.
+  delay(100);    // wait re-initialization of the 'Serial'
+#endif
+
+  //tasks
+  runner.addTask(hit_task);
+  runner.addTask(pcontrol_task);
+  runner.addTask(servo_release_task);
+}
+
+void loop() {
+  //
+  runner.execute();
+  //
+}

@osc/main_taskscheduler.cpp

@@ -0,0 +1,226 @@
+//
+// wirelessly connected cloud (Wireless Mesh Networking)
+//
+
+//
+// Conversations about the ROOT @ SEMA storage, Seoul
+//
+
+//
+// 2021 02 15
+//
+// (part-2) teensy35 : 'client:osc' (osc over slip --> mesh post)
+//
+
+//arduino
+#include <Arduino.h>
+
+//osc (already included in "framework-arduinoteensy")
+#include <OSCBundle.h>
+#include <SLIPEncodedUSBSerial.h>
+SLIPEncodedUSBSerial SLIPSerial(Serial);
+
+//post definition
+#include "../../post.h"
+
+//postman's uart
+#define POSTMAN_SERIAL  (Serial3)
+
+//
+void midinote(OSCMessage& msg, int offset) {
+  // matches will happen in the order. that the bundle is packed.
+  static int pitch = 0;
+  static int velocity = 0;
+  static int onoff = 0;
+  static int x1 = 0;
+  static int x2 = 0;
+  static int x3 = 0;
+  static int x4 = 0;
+  static int ps = 0;
+  // (1) --> /onoff
+  if (msg.fullMatch("/onoff", offset)) {
+    //
+    pitch = 0;
+    velocity = 0;
+    onoff = 0;
+    //
+    onoff = msg.getInt(0);
+    if (onoff != 0) onoff = 1;
+  }
+  // (2) --> /velocity
+  if (msg.fullMatch("/velocity", offset)) {
+    velocity = msg.getInt(0);
+    if (velocity < 0) velocity = 0;
+    // if (velocity > 127) velocity = 127;
+    if (velocity > 999) velocity = 999;
+  }
+  // (3) --> /pitch
+  if (msg.fullMatch("/pitch", offset)) {
+    pitch = msg.getInt(0);
+    if (pitch < 0) pitch = 0;
+    // if (pitch > 127) pitch = 127;
+    if (pitch > 999) pitch = 999;
+  }
+  // (4) --> /x
+  if (msg.fullMatch("/x", offset)) {
+    x1 = msg.getInt(0);
+    x2 = msg.getInt(1);
+    x3 = msg.getInt(2);
+    x4 = msg.getInt(3);
+    ps = msg.getInt(4);
+
+    char letter[POST_BUFF_LEN] = "";
+    snprintf(letter, POST_BUFF_LEN, "[%03d%03d%01dX%05d%05d%05d%05d%02d]",
+             pitch,
+             velocity,
+             onoff,
+             x1,
+             x2,
+             x3,
+             x4,
+             ps);
+    POSTMAN_SERIAL.print(letter);
+  }
+}
+
+//task
+#include <TaskScheduler.h>
+Scheduler runner;
+void osc_listen () {
+  //
+  static OSCBundle bundleIN;
+  int size = 0;
+  while (!SLIPSerial.endofPacket()) {
+    if ((size = SLIPSerial.available()) > 0) {
+      while(size--) {
+        bundleIN.fill(SLIPSerial.read());
+      }
+    }
+  }
+  //
+  if(!bundleIN.hasError()) {
+    bundleIN.route("/note", midinote);
+    //
+    bundleIN.empty();
+  }
+}
+Task osc_listen_task(0, TASK_FOREVER, osc_listen, &runner, true); // aInterval == 0 >>> immediately re-schedule ?
+//
+// OSCBundle bundleIN;
+// int size;
+//
+// while(!SLIPSerial.endofPacket())
+//   if( (size =SLIPSerial.available()) > 0)
+//   {
+//     while(size--)
+//       bundleIN.fill(SLIPSerial.read());
+//   }
+//
+// if(!bundleIN.hasError())
+//   bundleIN.dispatch("/led", LEDcontrol);
+//
+
+void postman_talk () {
+  //
+  static bool insync = false;
+  if (insync == false) {
+    int size;
+    if ((size = POSTMAN_SERIAL.available()) > 0) {
+      char last = '.';
+      while(size--) {
+        // get the last byte
+        last = POSTMAN_SERIAL.read();
+      }
+      // expectable last of the messages
+      if (last == ']' || last == '}') {
+        insync = true;
+      }
+    }
+  } else if (insync == true) {
+
+    if (POSTMAN_SERIAL.available() > POST_LENGTH) {
+      char cstr[POST_BUFF_LEN] = "................................";
+      // fetch all the bytes
+      POSTMAN_SERIAL.readBytes(cstr, POST_LENGTH);
+      // protocol checks
+      char first = cstr[0];
+      char last = cstr[POST_LENGTH-1];
+      if (first != '[' && first != '{') {
+        insync = false;
+        return;   //error!!
+      }
+      if (last != ']' && last != '}') {
+        insync = false;
+        return;   //error!!
+      }
+
+      //// OK -> parse && compose & send OSC message!
+
+      String msg = String(cstr);
+
+      // hello frame ( '{' + 30 bytes + '}' )
+      //    : {123456789012345678901234567890}
+
+      // hello frame
+      //    : {123456789012345678901234567890}
+      //    : {IIIA111111222222333333444444__}
+      //    : III - ID_KEY
+      //      .substring(1, 4);
+      //    : 1 - data of 6 letters
+      //      .substring(9, 14);
+      //    : 2 - data of 6 letters
+      //      .substring(14, 19);
+      //    : 3 - data of 6 letters
+      //      .substring(19, 24);
+      //    : 4 - data of 6 letters
+      //      .substring(24, 29);
+
+      // received a hello.
+      String str_id = msg.substring(1, 4);
+      int id = str_id.toInt();
+
+      //
+      OSCMessage hello("/hello");
+      hello.add(id);
+
+      //
+      String str_aa = msg.substring(4, 5);
+
+      //
+      if (str_aa == "A") {
+        //
+        String str_h1 = msg.substring(5, 11);
+        String str_h2 = msg.substring(11, 17);
+        String str_h3 = msg.substring(17, 23);
+        String str_h4 = msg.substring(23, 29);
+
+        //
+        hello.add(str_h1.toInt());
+        hello.add(str_h2.toInt());
+        hello.add(str_h3.toInt());
+        hello.add(str_h4.toInt());
+      }
+
+      //
+      SLIPSerial.beginPacket();
+      hello.send(SLIPSerial);
+      SLIPSerial.endPacket();
+      hello.empty();
+    }
+  }
+}
+Task postman_talk_task(0, TASK_FOREVER, postman_talk, &runner, true); // aInterval == 0 >>> immediately re-schedule ?
+
+//
+void setup() {
+  //osc
+  SLIPSerial.begin(57600);
+
+  //
+  POSTMAN_SERIAL.begin(115200);
+}
+
+//
+void loop() {
+  runner.execute();
+}

@osc/platformio.ini

@@ -0,0 +1,30 @@
+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[platformio]
+env_default = teensy36
+
+[common]
+lib_deps =
+  721@3.0.2 ; TaskScheduler
+
+; osc -> (already included in "framework-arduinoteensy")
+
+[env:teensy35]
+platform = teensy@3.6.0
+board = teensy35
+framework = arduino
+lib_deps = ${common.lib_deps}
+
+[env:teensy36]
+platform = teensy@3.6.0
+board = teensy36
+framework = arduino
+lib_deps = ${common.lib_deps}

@osc/src/main.cpp

@@ -0,0 +1,159 @@
+//
+// wirelessly connected cloud (based on ESP-NOW, a kind of LPWAN?)
+//
+
+//
+// Conversations about the ROOT @ SEMA storage, Seoul
+//
+
+//
+// 2021 02 15
+//
+// (part-2) teensy35 : 'client:osc' (osc over slip <--> esp-now 'post')
+//
+
+//arduino
+#include <Arduino.h>
+
+//osc (already included in "framework-arduinoteensy")
+#include <OSCBundle.h>
+#include <SLIPEncodedUSBSerial.h>
+SLIPEncodedUSBSerial SLIPSerial(Serial);
+
+//post definition
+#include "../../post.h"
+
+//postman's uart
+#define POSTMAN_SERIAL  (Serial3)
+
+//
+void setup() {
+  //osc
+  SLIPSerial.begin(57600);
+
+  //
+  POSTMAN_SERIAL.begin(115200);
+}
+
+//
+void route_note(OSCMessage& msg, int offset) {
+  // matches will happen in the order. that the bundle is packed.
+  static Note note;
+  // (1) --> /onoff
+  if (msg.fullMatch("/onoff", offset)) {
+    //
+    note.clear();
+    //
+    note.onoff = msg.getFloat(0);
+    if (note.onoff != 0) note.onoff = 1;
+  }
+  // (2) --> /velocity
+  if (msg.fullMatch("/velocity", offset)) {
+    note.velocity = msg.getFloat(0);
+  }
+  // (3) --> /pitch
+  if (msg.fullMatch("/pitch", offset)) {
+    note.pitch = msg.getFloat(0);
+  }
+  // (4) --> /id
+  if (msg.fullMatch("/id", offset)) {
+    note.id = msg.getInt(0);
+  }
+  // (5) --> /x
+  if (msg.fullMatch("/x", offset)) {
+    note.x1 = msg.getFloat(0);
+    note.x2 = msg.getFloat(1);
+    note.x3 = msg.getFloat(2);
+    note.x4 = msg.getFloat(3);
+    note.ps = msg.getFloat(4);
+    //
+    POSTMAN_SERIAL.write('['); // start byte of 'Note'
+    POSTMAN_SERIAL.write((uint8_t *) &note, sizeof(Note));
+    POSTMAN_SERIAL.write(']'); // end byte of 'Note'
+    //
+  }
+}
+
+//
+void loop() {
+
+  //osc
+  OSCBundle bundleIN;
+  int size;
+  if (SLIPSerial.available()) {
+    while(!SLIPSerial.endofPacket()) {
+      if( (size = SLIPSerial.available()) > 0) {
+        while(size--) {
+          bundleIN.fill(SLIPSerial.read());
+        }
+      }
+    }
+    if(!bundleIN.hasError()) {
+      // on '/note'
+      bundleIN.route("/note", route_note);
+    }
+  }
+
+  //postman (serial comm.)
+  static bool insync = false;
+  if (insync == false) {
+    while (POSTMAN_SERIAL.available() > 0) {
+      // search the last byte
+      char last = POSTMAN_SERIAL.read();
+      // expectable last of the messages
+      if (last == ']' || last == '}') {
+        insync = true;
+      }
+    }
+  } else {
+    //
+    if (POSTMAN_SERIAL.available() > 0) {
+      //
+      char type = POSTMAN_SERIAL.peek();
+      //
+      if (type == '{') {
+        //expecting a Hello message.
+        if (POSTMAN_SERIAL.available() > sizeof(Hello) + 2) {
+          POSTMAN_SERIAL.read();
+          //
+          Hello hello("");
+          POSTMAN_SERIAL.readBytes((uint8_t *) &hello, sizeof(Hello));
+          char last = POSTMAN_SERIAL.read();
+          if (last == '}') {
+            //good.
+            //
+            OSCMessage osc("/hello");
+            osc.add(hello.id);
+            osc.add(hello.h1);
+            osc.add(hello.h2);
+            osc.add(hello.h3);
+            osc.add(hello.h4);
+            //
+            SLIPSerial.beginPacket();
+            osc.send(SLIPSerial);
+            SLIPSerial.endPacket();
+            osc.empty();
+            //
+          } else {
+            insync = false; //error!
+          }
+        }
+      } else if (type == '[') {
+        //expecting a Note message.
+        if (POSTMAN_SERIAL.available() > sizeof(Note) + 2) {
+          POSTMAN_SERIAL.read();
+          //
+          Note note;
+          POSTMAN_SERIAL.readBytes((uint8_t *) &note, sizeof(Note));
+          char last = POSTMAN_SERIAL.read();
+          if (last == ']') {
+            //good.
+          } else {
+            insync = false; //error!
+          }
+        }
+        //
+      }
+    }
+  }
+}

@postman/platformio.ini

@@ -0,0 +1,52 @@
+; < NOTE >
+
+; to enable verbose output add option -->
+; $ platformio run --verbose
+
+; to make this permanent for the proj. -->
+; $ platformio settings set force_verbose Yes
+
+; then confirm the change -->
+; $ platformio settings get
+
+
+; // pio v 4.0 'Build options'
+;    - build_type
+;    - build_flags
+;    - src_build_flags
+;    - build_unflags
+;    - src_filter
+;    - targets
+
+
+[platformio]
+default_envs = d1_mini_pro
+
+[env]
+framework = arduino
+upload_port = /dev/ttyUSB0
+lib_deps =
+;  SPI
+;  Wire
+  721 ; TaskScheduler
+
+[env:nodemcuv2]
+platform = espressif8266
+board = nodemcuv2
+lib_deps =
+  ${env.lib_deps}
+upload_speed = 921600 ; 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600
+
+[env:d1_mini_pro]
+platform = espressif8266
+board = d1_mini_pro
+lib_deps =
+  ${env.lib_deps}
+upload_speed = 460800 ; 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600
+
+[env:huzzah]
+platform = espressif8266
+board = huzzah
+lib_deps =
+  ${env.lib_deps}
+upload_speed = 921600 ; 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600

@postman/src/main.cpp

@@ -0,0 +1,433 @@
+//
+// wirelessly connected cloud (based on ESP-NOW, a kind of LPWAN?)
+//
+
+//
+// Conversation about the ROOT @ SEMA storage, Seoul
+//
+
+//
+// 2021 02 15
+//
+// (part-1) esp8266 : 'postman' (the esp-now network nodes)
+//
+//   this module will be an esp-now node in a group.
+//       like, a bird in a group of birds.
+//
+//   esp-now @ esp8266 w/ broadcast address (FF:FF:FF:FF:FF:FF)
+//       always broadcasting. everyone is 'talkative'.
+//
+
+// then, let it save a value in EEPROM (object with memory=mind?)
+
+//============<identities>============
+//
+#define MY_GROUP_ID       (898989)
+#define MY_ID             (MY_GROUP_ID + 0)
+#define MY_SIGN           ("@POSTMAN|@SAMPLER")
+#define ADDRESSBOOK_TITLE ("broadcast only")
+//
+//============</identities>============
+
+//==========<list-of-configurations>===========
+//
+// 'HAVE_CLIENT'
+// --> i have a client. enable the client task.
+//
+// 'SERIAL_SWAP'
+// --> UART pin swapped.
+//     you want this, when you want a bi-directional comm. to external client boards (e.g. teensy).
+//
+// 'DISABLE_AP'
+// --> (questioning)...
+//
+// 'REPLICATE_NOTE_REQ' (+ N_SEC_BLOCKING_NOTE_REQ)
+// --> for supporting wider area with simple esp_now protocol,
+//     all receipents will replicate NOTE msg. when they are newly appeared.
+//   + then, network would be flooded by infinite duplicating msg.,
+//     unless they stop reacting to 'known' req. for some seconds. (e.g. 3 seconds)
+
+// 'HAVE_CLIENT_I2C'
+// --> i have a client w/ I2C i/f. enable the I2C client task.
+//
+// 'ADDRESSBOOK_TITLE'
+// --> peer list limited max. 20.
+//     so, we might use different address books for each node to cover a network of more than 20 nodes.
+//
+//==========</list-of-configurations>==========
+//
+#define HAVE_CLIENT_I2C
+#define DISABLE_AP
+// #define SERIAL_SWAP
+// #define REPLICATE_NOTE_REQ
+
+//============<parameters>============
+//
+#define LED_PERIOD (11111)
+#define LED_ONTIME (1)
+#define LED_GAPTIME (222)
+//
+#define WIFI_CHANNEL 1
+//
+// 'MONITORING_SERIAL'
+//
+// --> sometimes, the 'Serial' is in use (for example, 'osc' node)
+//     then,      use 'Serial1' - D4/GPIO2/TDX1 @ nodemcu (this is TX only.)
+//
+// --> otherwise, MONITORING_SERIAL == Serial.
+//
+#if defined(SERIAL_SWAP)
+#define MONITORING_SERIAL (Serial1)
+#else
+#define MONITORING_SERIAL (Serial)
+#endif
+//
+//============</parameters>===========
+
+//============<board-specifics>============
+#if defined(ARDUINO_FEATHER_ESP32) // featheresp32
+#define LED_PIN 13
+#else
+#define LED_PIN 2
+#endif
+//============</board-specifics>===========
+
+//arduino
+#include <Arduino.h>
+
+//i2c
+#include <Wire.h>
+
+//post & addresses
+#include "../../post.h"
+
+//vector
+#include <vector>
+std::vector<Note> recentNotes;
+
+//espnow
+#include <ESP8266WiFi.h>
+#include <espnow.h>
+AddressLibrary lib;
+
+//task
+#include <TaskScheduler.h>
+Scheduler runner;
+
+//
+#if defined(REPLICATE_NOTE_REQ)
+Note note_now = {
+  -1, // int32_t id;
+  -1, // float pitch;
+  -1, // float velocity;
+  -1, // float onoff;
+  -1, // float x1;
+  -1, // float x2;
+  -1, // float x3;
+  -1, // float x4;
+  -1 // float ps;
+};
+#define RECENT_NOTES_TIMEOUT (3000)
+static unsigned long last_note_time = 0;
+void recent_clear() {
+  //
+  if (millis() - last_note_time > RECENT_NOTES_TIMEOUT) {
+    recentNotes.clear();
+    Serial.println("recent list cleared");
+    last_note_time = millis();
+  }
+  //
+}
+Task recent_clear_task(100, TASK_FOREVER, &recent_clear, &runner, true);
+#endif
+//*-*-*-*-*-*-*-*-*-*-*-*-*
+
+//
+extern Task hello_task;
+static int hello_delay = 0;
+void hello() {
+  //
+  byte mac[6];
+  WiFi.macAddress(mac);
+  uint32_t mac32 = (((((mac[2] << 8) + mac[3]) << 8) + mac[4]) << 8) + mac[5];
+  //
+  Hello hello(String(MY_SIGN), MY_ID, mac32); // the most basic 'hello'
+  // and you can append some floats
+  static int count = 0;
+  count++;
+  hello.h1 = (count % 1000);
+  // hello.h2 = 0;
+  // hello.h3 = 0;
+  // hello.h4 = 0;
+  //
+  uint8_t frm_size = sizeof(Hello) + 2;
+  uint8_t frm[frm_size];
+  frm[0] = '{';
+  memcpy(frm + 1, (uint8_t *) &hello, sizeof(Hello));
+  frm[frm_size - 1] = '}';
+  //
+  esp_now_send(NULL, frm, frm_size); // to all peers in the list.
+  //
+  // MONITORING_SERIAL.write(frm, frm_size);
+  // MONITORING_SERIAL.println(" ==(esp_now_send/0)==> ");
+  //
+  if (hello_delay > 0) {
+    if (hello_delay < 100) hello_delay = 100;
+    hello_task.restartDelayed(hello_delay);
+  }
+}
+Task hello_task(0, TASK_ONCE, &hello, &runner, false);
+
+//task #0 : blink led
+extern Task blink_task;
+void blink() {
+  //
+  static int count = 0;
+  count++;
+  //
+  switch (count % 4) {
+  case 0:
+    digitalWrite(LED_PIN, LOW); // first ON
+    blink_task.delay(LED_ONTIME);
+    break;
+  case 1:
+    digitalWrite(LED_PIN, HIGH); // first OFF
+    blink_task.delay(LED_GAPTIME);
+    break;
+  case 2:
+    digitalWrite(LED_PIN, LOW); // second ON
+    blink_task.delay(LED_ONTIME);
+    break;
+  case 3:
+    digitalWrite(LED_PIN, HIGH); // second OFF
+    blink_task.delay(LED_PERIOD - 2* LED_ONTIME - LED_GAPTIME);
+    break;
+  }
+}
+Task blink_task(0, TASK_FOREVER, &blink, &runner, true); // -> ENABLED, at start-up.
+
+// on 'receive'
+void onDataReceive(uint8_t * mac, uint8_t *incomingData, uint8_t len) {
+
+  //
+  //MONITORING_SERIAL.write(incomingData, len);
+
+  //
+#if defined(HAVE_CLIENT)
+  Serial.write(incomingData, len); // we pass it over to the client.
+#endif
+
+  // open => identify => use.
+  if (incomingData[0] == '{' && incomingData[len - 1] == '}' && len == (sizeof(Hello) + 2)) {
+    Hello hello("");
+    memcpy((uint8_t *) &hello, incomingData + 1, sizeof(Hello));
+    //
+    MONITORING_SERIAL.println(hello.to_string());
+    //
+  }
+
+  // open => identify => use.
+  if (incomingData[0] == '[' && incomingData[len - 1] == ']' && len == (sizeof(Note) + 2)) {
+    Note note;
+    memcpy((uint8_t *) &note, incomingData + 1, sizeof(Note));
+
+    //is this for me & my client?
+    if (note.id == MY_GROUP_ID || note.id == MY_ID) {
+
+      #if defined(HAVE_CLIENT_I2C)
+      // (struct --> obsolete I2C format.)
+      //    --> we want to open & re-construct the msg.
+
+      // letter frame ( '[' + 30 bytes + ']' )
+      //    : [123456789012345678901234567890]
+
+      // 'MIDI' letter frame
+      //    : [123456789012345678901234567890]
+      //    : [KKKVVVG.......................]
+      //    : KKK - Key
+      //      .substring(1, 4);
+      //    : VVV - Velocity (volume/amp.)
+      //      .substring(4, 7);
+      //    : G - Gate (note on/off)
+      //      .substring(7, 8);
+
+      char letter_outro[POST_BUFF_LEN] = "................................";
+      if (note.pitch < 0) note.pitch = 0;
+      if (note.pitch >= 1000) note.pitch = 999;
+      if (note.velocity < 0) note.velocity = 0;
+      if (note.velocity >= 1000) note.velocity = 999;
+      if (note.onoff < 0) note.onoff = 0;
+      if (note.onoff >= 10) note.onoff = 9;
+      sprintf(letter_outro, "[%03d%03d%01d.......................]",
+              (int32_t)note.pitch,
+              (int32_t)note.velocity,
+              (int32_t)note.onoff);
+      String msg = String(letter_outro);
+
+      // truncate any extra. letters.
+      msg = msg.substring(0, POST_LENGTH); // (0) ~ (POST_LENGTH-1)
+
+      // send out
+      Wire.beginTransmission(I2C_ADDR);
+      Wire.write(msg.c_str(), POST_LENGTH);
+      Wire.endTransmission();
+
+      #endif
+      //
+      hello_delay = note.ps;
+      if (hello_delay > 0 && hello_task.isEnabled() == false) {
+        hello_task.restart();
+      }
+    }
+
+    //
+    MONITORING_SERIAL.println(note.to_string());
+
+    #if defined(REPLICATE_NOTE_REQ)
+    last_note_time = millis(); //clear timer reset : the recent list holding (re)started
+    // check if this note is in the list?
+    bool check = false;
+    for (uint32_t idx = 0; idx < recentNotes.size(); idx++) {
+      if (recentNotes[idx].pitch == note.pitch && recentNotes[idx].id == note.id) {
+        check = true;
+      }
+    }
+    // if not, add this into the list and repeat!
+    if (check == false) {
+      //
+      recentNotes.push_back(note);
+      //
+      uint8_t frm_size = sizeof(Note) + 2;
+      uint8_t frm[frm_size];
+      frm[0] = '[';
+      memcpy(frm + 1, (uint8_t *) &note, sizeof(Note));
+      frm[frm_size - 1] = ']';
+      //
+      esp_now_send(NULL, frm, frm_size); // to all peers in the list.
+      //
+      MONITORING_SERIAL.print("repeat! ==> ");
+      MONITORING_SERIAL.println(note.to_string());
+      //
+    }
+
+    //EMERGENCY PATCH.HACK:
+    // original code is not intended for a BURST of notes.
+    // so, only 1 msg. will be repeated in 3 sec. all others will be simply ignored.
+    // to make a burst of msgs repeatible:
+    // --> make a list of recent 'pitches'
+    //     if there is any new msg. check if this is in the list, if not, add it & repeat, if yes, skip it.
+    //     after 3sec no new msg., the list will be flushed. every new msg. will reset timeout + save the list for extra. 3 sec.
+    #endif
+  }
+}
+
+// on 'sent'
+void onDataSent(uint8_t *mac_addr, uint8_t sendStatus) {
+  char buff[256] = "";
+  sprintf(buff, "Delivery failed! -> %02X:%02X:%02X:%02X:%02X:%02X",  mac_addr[0],  mac_addr[1],  mac_addr[2],  mac_addr[3],  mac_addr[4],  mac_addr[5]);
+  if (sendStatus != 0) MONITORING_SERIAL.println(buff);
+}
+
+//
+void setup() {
+
+  //led
+  pinMode(LED_PIN, OUTPUT);
+
+  //serial
+  Serial.begin(115200);
+  delay(100);
+
+  //info
+  Serial.println();
+  Serial.println();
+  Serial.println("\"hi, i m your postman.\"");
+  Serial.println("-");
+  Serial.println("- my id: " + String(MY_ID) + ", gid: " + String(MY_GROUP_ID) + ", call me ==> \"" + String(MY_SIGN) + "\"");
+  Serial.println("- mac address: " + WiFi.macAddress() + ", channel: " + String(WIFI_CHANNEL));
+#if defined(HAVE_CLIENT)
+  Serial.println("- ======== 'HAVE_CLIENT' ========");
+#endif
+#if defined(SERIAL_SWAP)
+  Serial.println("- ======== 'SERIAL_SWAP' ========");
+#endif
+#if defined(DISABLE_AP)
+  Serial.println("- ======== 'DISABLE_AP' ========");
+#endif
+#if defined(HAVE_CLIENT_I2C)
+  Serial.println("- ======== 'HAVE_CLIENT_I2C' ========");
+#endif
+#if defined(REPLICATE_NOTE_REQ)
+  Serial.println("- ======== 'REPLICATE_NOTE_REQ' ========");
+#endif
+  Serial.println("-");
+
+  //wifi
+  WiFiMode_t node_type = WIFI_AP_STA;
+#if defined(DISABLE_AP)
+  system_phy_set_max_tpw(0);
+  node_type = WIFI_STA;
+#endif
+  WiFi.mode(node_type);
+
+  //esp-now
+  if (esp_now_init() != 0) {
+    Serial.println("Error initializing ESP-NOW");
+    return;
+  }
+#if defined(ESP8266)
+  esp_now_set_self_role(ESP_NOW_ROLE_COMBO);
+#endif
+  esp_now_register_send_cb(onDataSent);
+  esp_now_register_recv_cb(onDataReceive);
+  //
+
+  AddressBook * book = lib.getBookByTitle(ADDRESSBOOK_TITLE);
+  if (book == NULL) {
+    Serial.println("- ! wrong book !! : \"" + String(ADDRESSBOOK_TITLE) + "\""); while(1);
+  }
+  for (int idx = 0; idx < book->list.size(); idx++) {
+    Serial.println("- ! (esp_now_add_peer) ==> add a '" + book->list[idx].name + "'.");
+#if defined(ESP32)
+    esp_now_peer_info_t peerInfo = {};
+    memcpy(peerInfo.peer_addr, book->list[idx].mac, 6);
+    peerInfo.channel = 0;
+    peerInfo.encrypt = false;
+    esp_now_add_peer(&peerInfo);
+#else
+    esp_now_add_peer(book->list[idx].mac, ESP_NOW_ROLE_COMBO, 1, NULL, 0);
+#endif
+  }
+  // (DEBUG) fetch full peer list
+  { PeerLister a; a.print(); }
+  //
+  Serial.println("-");
+  Serial.println("\".-.-.-. :)\"");
+  Serial.println();
+
+#if defined(SERIAL_SWAP)
+  Serial.println("-      ======== 'SERIAL_SWAP' ========");
+  // a proper say goodbye.
+  Serial.println("\"bye, i will do 'swap' in 1 second. find me on alternative pins!\"");
+  Serial.println("\"    hint: osc wiring ==> esp8266(serial.swap) <-> teensy(serial3)\"");
+  Serial.println("-");
+  Serial.println("\".-.-.-. :)\"");
+  delay(1000);   // flush out unsent serial messages.
+
+  // moving...
+  Serial.swap(); // use RXD2/TXD2 pins, afterwards.
+  delay(100);    // wait re-initialization of the 'Serial'
+#endif
+
+  //
+#if defined(HAVE_CLIENT_I2C)
+  //i2c master
+  Wire.begin();
+#endif
+}
+
+void loop() {
+  //
+  runner.execute();
+  //
+}