PROCESSOR-SDK-AM62X: How to move data in spidev_test.c?

Daniel Cheng1

Mastermind 7075 points

Part Number: PROCESSOR-SDK-AM62X

Tool/software:

Hi Expert,

The customer is currently using the default spidev_test.c file and has not changed the content.

Does spidev_test.c use FIFO or DMA to move data through SPI? (We hope to use FIFO)

Thanks

Daniel

4 months ago

0 Andreas Dannenberg 4 months ago

TI__Guru 69622 points

Hi Daniel

Daniel Cheng1 said:
Does spidev_test.c use FIFO or DMA to move data through SPI? (We hope to use FIFO)

whether FIFO and/or DMA is used depends on the Kernel driver, how it is configured, and the size of the SPI transfer. It is not under direct control of userspace applications such as the spidev_test.c application.

Specifically, as for our current SDK v11.x (based on Linux Kernel 6.12), the following applies:

FIFO is used when the use of DMA is configured via Device Tree and the SPI transfer length is at least 160 bytes
FIFO is not used when the DMA is not configured or the SPI transfer length is less than 160 bytes

For more information on how to configure the use of DMA and to update the minimum transfer length, see here: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1356551/faq-am6x-optimizing-spi-transfer-inter-byte-gaps-using-the-dma-in-linux

Usually the use of DMA helps to reduce (but not eliminate) the "inter-byte gaps" observed during SPI master operation.

Regards, Andreas

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PROCESSOR-SDK-AM62X: How to move data in spidev_test.c?