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What is the maximum speed to write to an SD card with SDIO in 4Bit mode and how to reach it

Question asked by Andreas S. on Aug 25, 2017
Latest reply on Aug 28, 2017 by avi_crak.videocrak

Hi all,

I am trying to get a hight speed write to SD via SDIO as well. I use a project generated with Cube MX, 4bit SDIO and DMA. But I only get a write speed of about 300 kBytes/s. I write 1000 times a 100 byte block, because I need a write about every 100 us. With a 100 byte block I have a write time of about 25 us, but every fifth time over 1 ms. Weird...The time span to the 1 ms write decreases the less bytes I write.

When I look at the trace of TrueStudio, I see that more than 60% of the time is spend in the function SDMMC_GetCmdResp1, compared to only 0.05% in BSP_SD_WriteBlocks_DMA... (Screenshot attached)

I am running it on a STM32f429IGT at 180MHz with 8MHz external crystal. My clocksettings for the main clocks are 8MHz HSE, M=8, N=360, P=2, AHB Pre=1, APB1 Pre =4 and APB2=2 -> 90 MHz -> its this to high?.

Clocksetting for SDIO is 0, as CubeMX advises.

What would the max speed be for a write to SD card via SDIO?

I use a 16Gig SD card with SpeedClass 10 from SanDisk.

I have played around with some settings of FatFs, e.g. set the _MIN_SS and _MAX_SS to 4096, then I have a write speed of about 2MBit/s, but the card is not readable in Windows anymore.

I have tried another example from the CubeLib V1.16/Projects/STM324xx9I_EVAL/Applications/FatFs/FatFs_uSD, copied the write loop from the previous project and had a write speed of about 1 MByte/s - yesterday. Today I tried to compile it with optimize level 2 and now I have the same write speed like in the previous project, of about 300kByte/s. This is weird.

Has anyone an example?

Thanks a lot,

best regards

Andreas

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