Summary

The following code does not work with NUCLEO-F767ZI.
Incorrect wave may be output on PA4. STM32H7 has same issue.

import math
from pyb import DAC

# 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(1, bits=8)
dac.write_timed(buf, 600 * len(buf), mode=DAC.CIRCULAR)

For MCUs which has D-Cache (such as STM32F7, STM32H7), clean D-cache before starting DMA.
For more details, please refer follwing document:
https://www.st.com/resource/en/application_note/DM00272913.pdf

This PR cleans D-cache before starting DMA.

Testing

Tested code above with:

• NUCLEO-F767ZI (STM32F767ZI)
• WeAct H743VI (STM32H743VI, PR: stm32/boards: Add WeAct_H743VI board support. #17766)

-> Both boards output wave as expected.