Hello,
I'm trying to transfer a 4000 uint16_t buffer from SRAM4 to DTCM. This is working with a basic configuration of the MDMA module :
- Buf size = 32
- Block len = 4000
- No burst mode
- in/out size = half word.
The MDMA needs 135µs to transfer the whole buffer, and it looks quite slow. I'm questioning about the different way to improve the tranfer, using burst mode and/or packed mode.
When implementing the burst mode, I have a strange behavior of the MDMA initialization.
hmdma_mdma_channel0_sw_0.Instance = MDMA_Channel0;
hmdma_mdma_channel0_sw_0.Init.Request = MDMA_REQUEST_SW;
hmdma_mdma_channel0_sw_0.Init.TransferTriggerMode = MDMA_BLOCK_TRANSFER;
hmdma_mdma_channel0_sw_0.Init.Priority = MDMA_PRIORITY_VERY_HIGH;
hmdma_mdma_channel0_sw_0.Init.Endianness = MDMA_LITTLE_ENDIANNESS_PRESERVE;
hmdma_mdma_channel0_sw_0.Init.SourceInc = MDMA_SRC_INC_HALFWORD;
hmdma_mdma_channel0_sw_0.Init.DestinationInc = MDMA_DEST_INC_HALFWORD;
hmdma_mdma_channel0_sw_0.Init.SourceDataSize = MDMA_SRC_DATASIZE_HALFWORD;
hmdma_mdma_channel0_sw_0.Init.DestDataSize = MDMA_DEST_DATASIZE_HALFWORD;
hmdma_mdma_channel0_sw_0.Init.DataAlignment = MDMA_DATAALIGN_PACKENABLE;
hmdma_mdma_channel0_sw_0.Init.BufferTransferLength = 32;
hmdma_mdma_channel0_sw_0.Init.SourceBurst = MDMA_SOURCE_BURST_128BEATS;
hmdma_mdma_channel0_sw_0.Init.DestBurst = MDMA_DEST_BURST_128BEATS;
If running in debug mode, the live watch of MDMA_C0TCR.SBURST/DBUST shows 0 and the transfer is slow.
If running the HAL init function of MDMA in step-by-step mode, MDMA_C0TCR is correctly initialized. After what running the program works fine and the transfer time is really reduced (85µs)
I have similar init issues if trying to use packet mode, and in all cases with the TRGM bit : The register init is ok when debuging step-by-step, and wrong if running the program.
Is there a real issue or is it another dirty trick of the complex superscalar Cortex-M7 architecture ?
I'm not watching the register immediately after the write, but a long time after, to get rid of the propagation time between trough the different busses.
Any help appreciated :)
Thanks
