This post collects observations when using MAix GO board with Arduino IDE, call Maixduino.

Macros how special pins on board MAix GO are called, can be found in pins_arduino.h of MAix GO., like PIN_KEY_PRESS which has an external pull up resistor (see schematic).

When testing example code of libraries function Serial.begin() seems to need a little time to initialize. Console output worked after adding 300mS delay. (How much is the minimal delay required?):

Serial.begin(115200);
delay(300);

Below libraries are listed which have example code that compiles and runs with MAix GO board (maybe the code needs minimal modification like replacing BUILTIN_LED by LED_BUILTIN; use compiler error messages – Preferences/Show verbose output during compilation):

  • WiFiEsp (included with Maixduino board addon of Arduino IDE)
  • RingBuffer by locoduino (installable with Arduino Library Manager)
    (Maybe EspRingBuffer coming as part of of WiFiEsp bundled with Maixduino, folder src/utility, is of interest as well.)
  • ArduinoJson by Benoît Blanchan (Arduino Library Manager)
  • ArduinoMqtt by Oleg Kovalenk which is based on eclipse paho (Arduino Library Manager)
    Use the example ConnectEsp8266WiFiClient and replace: ESP8266WiFi.h by WiFiEsp.h (included in Maixduino), WiFiClient by WiFiEspClient, ESP.reset() by WiFi.reset() and copy WiFi setup code from example of WiFiEsp. – If not properly initialized might stop k210 cpu with illegal instruction.
  • pubsubclient by Nick O’Leary (Arduino Library Manager). Same remarks as shown above (ArduinoMqtt).

According to Kendryte K210 datasheet (available here) the speed of the 4 uart interfaces of K210 can run with up to 5 MHz baud rate. Communication with esp8285 used as wifi chip runs by default with 115200 baud and seems to run with 2000000 baud as well. (Tested with sketch Examples/Maix Go/WiFiEsp/Test/EspDebug: use command AT+UART_CUR:2000000,8,1,0,1). AT command reference is here. Using the _CUR command means that after reboot the default settings get restored. Storing the settings permanently bears the risk to make esp8266 inaccessible (if not reflashed).

Source of AT command firmware is here at github, if you select tag v2.2.1 (examples/at). – Install compiler (folder dist in https://github.com/noduino/xtensa-toolchain or http://domoticx.com/sdk-esp8266-xtensa-architecture-toolchain/) and add it to path. Inside SDK folder copy folder examples/at to root folder of SDK. Run script gen_misc and choose: boot_v1.2+, user1.bin (or user2.bin), spi 40MHz, spi DOUT, 1024KB (512KB+512KB); result is in folder bin/. Uploading to esp8285 would require to shorten ground and the pad GPIO0 in the corner of the antenna connector (info from sipeed forum).

notes about using esptool.py to flash firmware (hide expanded file):
to verify size of flash
python utils/esptool.py --port /dev/cu.usbserial-143110 --baud 115200 flash_id

nodemcu board, 4MB=32000kbit, successfully flashed with
python utils/esptool.py --port /dev/cu.usbserial-143110 --baud 115200 write_flash 0x00000 bin/eagle.flash.bin 0x10000 bin/eagle.irom0text.bin 0x7E000 bin/blank.bin 0x3FE000 bin/blank.bin 0x3FC000 bin/esp_init_data_default.bin 
(tested by konsole of arduino ide; firmware has default baud rate of 115200; boot messages are sent with 74880 baud ->technical reference of esp8266)

esp8285, 1MB=4096kbit, should be flashable with
python utils/esptool.py --port /dev/cu.usbserial-143110 --baud 115200 write_flash 0x00000 bin/eagle.flash.bin 0x10000 bin/eagle.irom0text.bin 0x7E000 bin/blank.bin 0xFE000 bin/blank.bin 0xFC000 bin/esp_init_data_default.bin

To use WiFiEsp lib with 2000000 baud without setting it permanently WiFiEsp has to be patched: by default WiFi.init(&Serial1) function does call AT+RST which reboots esp8285. In patched version you can call WiFi.init(&Serial1, false) to avoid this reboot:

WiFiEsp_disable_at_rst_in_init.diff (hide expanded diff file):
diff -ur orig/WiFiEsp.cpp new/WiFiEsp.cpp
--- orig/WiFiEsp.cpp	2019-07-15 17:14:20.000000000 +0200
+++ new/WiFiEsp.cpp	2019-08-07 11:32:14.000000000 +0200
@@ -33,8 +33,14 @@
 
 void WiFiEspClass::init(Stream* espSerial)
 {
+	init(espSerial, true);
+}
+
+
+void WiFiEspClass::init(Stream* espSerial, bool run_at_rst)
+{
     LOGINFO(F("Initializing ESP module"));
-	EspDrv::wifiDriverInit(espSerial);
+	EspDrv::wifiDriverInit(espSerial, run_at_rst);
 }
 
 
diff -ur orig/WiFiEsp.h new/WiFiEsp.h
--- orig/WiFiEsp.h	2019-07-15 17:14:20.000000000 +0200
+++ new/WiFiEsp.h	2019-08-07 11:33:01.000000000 +0200
@@ -51,6 +51,8 @@
 	*/
 	static void init(Stream* espSerial);
 
+	static void init(Stream* espSerial, bool do_at_rst);
+
 
 	/**
 	* Get firmware version
diff -ur orig/utility/EspDrv.cpp new/utility/EspDrv.cpp
--- orig/utility/EspDrv.cpp	2019-07-15 17:14:20.000000000 +0200
+++ new/utility/EspDrv.cpp	2019-08-07 12:04:48.000000000 +0200
@@ -70,8 +70,15 @@
 uint8_t EspDrv::_remoteIp[] = {0};
 
 
+
 void EspDrv::wifiDriverInit(Stream *espSerial)
 {
+	wifiDriverInit(espSerial, true);
+}
+
+
+void EspDrv::wifiDriverInit(Stream *espSerial, bool run_at_rst)
+{
 	LOGDEBUG(F("> wifiDriverInit"));
 
 	EspDrv::espSerial = espSerial;
@@ -95,7 +102,7 @@
 		return;
 	}
 
-	reset();
+	reset(run_at_rst);
 
 	// check firmware version
 	getFwVersion();
@@ -114,13 +121,23 @@
 }
 
 
+
 void EspDrv::reset()
 {
+	reset(true);
+}
+
+
+void EspDrv::reset(bool run_at_rst)
+{
 	LOGDEBUG(F("> reset"));
 
-	sendCmd(F("AT+RST"));
-	delay(3000);
-	espEmptyBuf(false);  // empty dirty characters from the buffer
+	if(run_at_rst)
+	{
+		sendCmd(F("AT+RST"));
+		delay(3000);
+		espEmptyBuf(false);  // empty dirty characters from the buffer
+	}
 
 	// disable echo of commands
 	sendCmd(F("ATE0"));
diff -ur orig/utility/EspDrv.h new/utility/EspDrv.h
--- orig/utility/EspDrv.h	2019-07-15 17:14:20.000000000 +0200
+++ new/utility/EspDrv.h	2019-08-07 11:38:57.000000000 +0200
@@ -123,6 +123,9 @@
     static void wifiDriverInit(Stream *espSerial);
 
 
+    static void wifiDriverInit(Stream *espSerial, bool run_at_rst);
+
+
     /* Start Wifi connection with passphrase
      *
      * param ssid: Pointer to the SSID string.
@@ -279,6 +282,8 @@
 	static bool ping(const char *host);
     static void reset();
 
+    static void reset(bool do_at_rst);
+
     static void getRemoteIpAddress(IPAddress& ip);
     static uint16_t getRemotePort();
 

To be continued.

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