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: Fix 12bit DAC issue on STM32H5.

mergedby yn386opened 2025-07-22updated 2025-08-18

port-stm32

Summary

The following code does not work with NUCLEO-H563ZI.

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(2, bits=12)
dac.write_timed(buf, 400 * len(buf), mode=DAC.CIRCULAR)

For STM32H5, DMA parameter should set:

Actual DMA source datawidth to CTR1.
The length is the amount of data to be transferred from source to destiniation in bytes. to use 12bit DAC.

Also, this PR modifies the definition of DMA_CIRCULAR for STM32H5 to prevent conflict with data width specification.

Testing

Tested code above with NUCLEO-H563ZI.
Also, DAC with 8bit still works after applying this PR.

Trade-offs and Alternatives

The value of DAC_CIRCULAR is changed:
from

>>> hex(DAC.CIRTUCLAR)
'0x1'

>>> hex(DAC.CIRCULAR)
'0x20000000'

Indeed, it won't be a problem because users do not need to be aware of value of DAC.CIRCULAR in most cases.