The S2 and S3 chips contain a RISCV ULP co-processor in addition to the FSM ULP.

This PR is an initial attempt to provide access to the RISCV co-processor from micropython.

Operation

1. During build cmake checks for the existence of file ports/esp32/ulp_riscv/main.c
2. main.c is compiled and included in the micropython firmware bin file
3. Calling ULP.riscv_load_binary() will load binary to ULP co-processor
4. Calling ULP.riscv_run() will run RISCV ULP.

Compilation

The ULP needs to be enabled in your sdkconfig.board

CONFIG_ESP32S3_ULP_COPROC_ENABLED=y
CONFIG_ESP32S3_ULP_COPROC_RISCV=y
CONFIG_ESP32S3_ULP_COPROC_RESERVE_MEM=4096

Build micropython as normal.

Example - Blinky

Tested with IDF v4.4.4, micropython latest

ports/esp32/ulp_riscv/main.c

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include "esp32s3/ulp_riscv.h"
#include "ulp_riscv/ulp_riscv_utils.h"
#include "ulp_riscv/ulp_riscv_gpio.h"

/* this variable will be exported as a public symbol, visible from main CPU: */
bool gpio_level = false;

int main (void)
{
   ulp_riscv_gpio_init(14);
   ulp_riscv_gpio_set_output_mode(14, RTCIO_MODE_OUTPUT);
   ulp_riscv_gpio_output_enable(14);

   while(1) {
   // Turn on GPIO
       ulp_riscv_gpio_output_level(14, 1);
       gpio_level = true;
   // Delay
       ulp_riscv_delay_cycles(1000 * 1000);
   // Turn off GPIO
       ulp_riscv_gpio_output_level(14, 0);
       gpio_level = false;
   // Delay
       ulp_riscv_delay_cycles(1000 * 1000);
   }

    /* ulp_riscv_halt() is called automatically when main exits */
    return 0;
}

MicroPython 3229791b6-dirty on 2023-05-20; INSIGHT_S3_GENERIC with ESP32-S3
Type "help()" for more information.
>>> import esp32
>>> ulp = esp32.ULP()
>>> ulp.riscv_load_binary()
>>> ulp.riscv_run()
>>>
>>> import machine
>>> machine.deepsleep(0)

After calling run() GPIO_14 will blink rapidly.

After entering deepsleep, GPIO_14 will continue to blink.

Sharing variables between ULP and main processor

Variables declared in the ULP code are made available in the main code using pointers to locations in the RTC memory. For example:

ULP code

bool gpio_level = false;

Micropython

>>> import esp32
>>> ulp = esp32.ULP()
>>> import machine
>>> machine.mem32[ulp.GPIO_LEVEL]
1
>>>  machine.mem32[ulp.GPIO_LEVEL] = 0
>>>

Next steps/improvements

• Support sharing variables between ULP and main program
• Documentation/examples
• Move main.c ULP code to more appropriate location, possibly to board definition sub-folder?
• Investigate if ULP programs can be compiled independently and uploaded to device, removing the need to re-flash device