QUERY · ISSUE

dac.write_timed() does not work with NUCLEO_G474RE

openby anchung-chenopened 2022-10-10updated 2023-07-01

bugport-stm32

The example code from micropython document does not work with NUCLEO_G474RE.

import math
from array import array
from pyb import DAC

# create a buffer containing a sine-wave, using half-word samples
buf = array('H', 2048 + int(2047 * math.sin(2 * math.pi * i / 128)) for i in range(128))

# output the sine-wave at 400Hz
dac = DAC(1, bits=12)
dac.write_timed(buf, 400 * len(buf), mode=DAC.CIRCULAR)

The DAC1 output of PA4 pin (A2 pin on arduino connector) shows no waveform.

After a little research, I found the root cause is that DMA_PDATAALIGN_WORD should be used for the "DMA + DAC" operation of STM32G4 cpu.

Here is my modification of dac.c to make dac.write_timed() work with NUCLEO_G474RE.

STATIC void dac_start_dma(uint32_t dac_channel, const dma_descr_t *dma_descr, uint32_t dma_mode, uint32_t bit_size, uint32_t dac_align, size_t len, void *buf) {
    uint32_t dma_align;
    if (bit_size == 8) {
        dma_align = DMA_MDATAALIGN_BYTE | DMA_PDATAALIGN_BYTE;
    } else {
#if defined(STM32G4)
        dma_align = DMA_MDATAALIGN_HALFWORD | DMA_PDATAALIGN_WORD;
#else
        dma_align = DMA_MDATAALIGN_HALFWORD | DMA_PDATAALIGN_HALFWORD;
#endif
    }

CANDIDATE · PULL REQUEST

stm32: Add DAC feature for STM32G0.

mergedby yn386opened 2025-07-25updated 2025-08-18

port-stm32

Summary

This PR adds DAC feature for STM32G0.
DAC.write() and DAC.write_timed() is now available.

Testing

The following code works with NUCLEO-G01BRE.
A sine wave is output via PA4 when ch=1, PA5 when ch=2.

import math
from pyb import DAC

ch = 1

# create a buffer containing a sine-wave
buf = bytearray(100)
for i in range(len(buf)):
    buf[i] = 128 + int(127 * math.sin(2 * math.pi * i / len(buf)))

# output the sine-wave at 600Hz
dac = DAC(ch, bits=8)
dac.write_timed(buf, 600 * len(buf), mode=DAC.CIRCULAR)

import math
from array import array
from pyb import DAC

ch = 2

# create a buffer containing a sine-wave, using half-word samples
buf = array('H', 2048 + int(2047 * math.sin(2 * math.pi * i / 128)) for i in range(128))

# output the sine-wave at 400Hz
dac = DAC(ch, bits=12)
dac.write_timed(buf, 400 * len(buf), mode=DAC.CIRCULAR)

Trade-offs and Alternatives

This PR increases code size by 1800 Bytes.

Before:

   text	   data	    bss	    dec	    hex	filename
 297528	    108	   4004	 301640	  49a48	build-NUCLEO_G0B1RE/firmware.elf

After:

   text	   data	    bss	    dec	    hex	filename
 299312	    108	   4020	 303440	  4a150	build-NUCLEO_G0B1RE/firmware.elf