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Macchina M2-B Hacking Notes

cli history `udevserial -v ID_MODEL=Arduino_Due -v SUBSYSTEM=tty` 115200 --raw
esptool32 --port `udevserial -v ID_MODEL=Arduino_Due -v SUBSYSTEM=tty` --before no_reset --after no_reset --baud 115200 write_flash 0x10000 ./build/gatt_server_demos.bin
#include <OBD2.h>
#include <DueTimer.h>
#include "SamNonDuePin.h"
bool led = 0;
bool toggleBootMode = false;
bool passThrough = false;
bool pipe = false;
const int XB_nRST = X4;
const int XB_GPIO0 = 56;
const int LED_YELLOW = X0;
int doDelay = 0;
void setup()
SerialUSB.println(printf("System Reset"));
SerialUSB.println("> ");
pinModeNonDue(XB_nRST, OUTPUT);
pinModeNonDue(XB_GPIO0, OUTPUT);
digitalWriteNonDue(XB_nRST, HIGH);
digitalWriteNonDue(XB_GPIO0, HIGH);
digitalWriteNonDue(LED_YELLOW, LOW);
// reboot ESP32 on startup
digitalWriteNonDue(XB_nRST, LOW);
toggleBootMode = true;
doDelay = 500;
void loop()
if(doDelay > 0) {
SerialUSB.print("Delay: ");
SerialUSB.print(".\n> ");
doDelay = 0;
if(toggleBootMode) {
digitalWriteNonDue(XB_nRST, HIGH);
toggleBootMode = false;
void serialEvent() {
// 'activity' light
digitalWriteNonDue(LED_YELLOW, led ? HIGH : LOW);
led = led ? 0 : 1;
// Serial data from XB_ can just be passed straight through
while(Serial.available()) {
void serialEventUSB() {
// 'activity' light
digitalWriteNonDue(LED_YELLOW, led ? HIGH : LOW);
led = led ? 0 : 1;
while(SerialUSB.available()) {
uint8_t c =;
if(pipe && c == 0x03) {
pipe = false;
SerialUSB.println("Ending pipe");
// if already in flash mode just write and stop
if(pipe || passThrough) {
// proper data coming back from ESP32 can be passed back
// simple command set
// b: enter boot mode
// r: reset
// both b and r lower nRST
// and toggle bootmode (back up in 500ms)
if(c == 'b' || c == 'r') {
SerialUSB.println("\n\nReseting ESP32");
digitalWriteNonDue(XB_nRST, LOW);
toggleBootMode = true;
doDelay = 500;
// b also lowers GPIO0 and enables pass-through
if(c == 'b') {
digitalWriteNonDue(XB_GPIO0, LOW);
passThrough = true;
} else if(c == 'p') {
SerialUSB.println("\nPiping data to ESP32");
pipe = true;
} else if(c == '\n') {
SerialUSB.print("> ");


Flashing the ESP32 was the first thing needing attention. I wanted to be able to flash the device without removing it from the socket.

Pass-through flashing

The plan. Put the ESP32 into flashmode via nRST GPIO0 toggling. Bring both LOW then bring nRST back up. Then esptool32 can be coerced into flashing the chip. There is still a bit of manual intervention but I got it working.


Using mac32.ino send b over the USB serial port to enter bootmode.

> b

Reseting ESP32
Delay: 500.
> ets Jun  8 2016 00:22:57

waiting for download

If using a serial terminal disconnect, there is nothing else to be done without resetting the M2.

Now you can start flashing the ESP32 with esptool32. The differences from normal use are the inclusion of --before no_reset and --after no_reset. You have to reset and re-enter bootmode for each file being flashed, this is a shortcoming in the code at the moment.

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