Safe Mode on esp32s2

[microdev1]

This is a follow-up to 9-9-20 (CPY Day) esp32s2 Deep Dive in which esp32s2 manual safe mode support was briefly discussed.

The esp32s2 posses a challenge for manual safe mode implementation as it lacks a dedicated reset pin instead the reset button is connected to CHIP_PU which when pulled low turns off the power to the chip thus causing a hard reset.

A solution to this problem as discussed during the deep dive is to use IO0 (boot button) and check its state during CPY startup in order to trigger a soft reboot keeping the ram alive.

I was able to boot into safe mode by pressing the boot button momentarily during 700ms loop which is indicated by a steady yellow color of the rgb led on startup.

As of now I am just returning MANUAL_SAFE_MODE instead of NO_SAFE_MODE in order to enter safe mode and haven't really figured how this will work alongside other CPY ports and how it will soft reboot with status stored in ram.

Code snippet from safe_mode.c .
Tested on microS2.

digitalio_digitalinout_obj_t boot_button;
common_hal_digitalio_digitalinout_construct(&boot_button, MICROPY_HW_BUTTON);  //#define MICROPY_HW_BUTTON (&pin_GPIO0) 
common_hal_digitalio_digitalinout_switch_to_input(&boot_button, PULL_UP);

uint64_t start_ticks = supervisor_ticks_ms64();
uint64_t diff = 0;

while (diff < 700) {
       #ifdef MICROPY_HW_LED_STATUS
       // Blink on for 100, off for 100, on for 100, off for 100 and on for 200
       common_hal_digitalio_digitalinout_set_value(&status_led, diff > 100 && diff / 100 != 2 && diff / 100 != 4);
       #endif
        
       if (!common_hal_digitalio_digitalinout_get_value(&boot_button)) {
           return MANUAL_SAFE_MODE;
       }

       diff = supervisor_ticks_ms64() - start_ticks;
}  

[tannewt]

Awesome! Thank you!

I think the easiest thing is to add a board define CIRCUITPY_BOOT_BUTTON that can be used to include the code you've added.

Want to make a PR? Thanks!

[microdev1]

@tannewt I'll leave this issue open until soft_reboot approach is also implemented.

[tannewt]

So we need to:

• Figure out how to reset from software and save 4-bytes across the reset.
• Detect brown outs and safe mode when it happens.
• Intercept fatal error from the IDF and safe mode.