AM623: How to configure the Main_SPI0 of AM623 as the host and the FPGA as the slave, and configure the Main_SPI0 of AM623 as the dma mode, and configure the passive receiving mode to actively read the data of the fpga buffer through dma after the fpga giv

Hi Bu,

some guidance on your question below...

bu yuying said:

How to configure the Main_SPI0 of AM623 as the host and the FPGA as the slave,

On the AM6x side what you'd probably want to do is the following, requiring some custom Kernel development:

1. Use an existing, preferably basic SPI peripheral driver as a baseline for your new driver. For this I'd recommend drivers/spi/spidev.c. It's basic and pretty well understood/used, and you can find resources including userspace access examples easily (e.g., ./tools/spi/spidev_test.c). Clone/copy this driver to a new file, and add a new CONFIG option and build support for your new file (need to edit Kconfig and Makefile in drivers/spi for that).
   
   
2. Add the related device tree entries. Also extend the main_spi0 DTS node to add the properties needed to enable DMA transfers. See here for details: 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
   
   
3. The last piece would be allowing the external FPGA to trigger an interrupt, so you know when to fetch data from the FPGA from Linux. One way to do that would be to leverage UIO (Userspace I/O) functionality of the Kernel, see https://www.kernel.org/doc/html/latest/driver-api/uio-howto.html. Basically look at an existing UIO driver like drivers/uio/uio_cif.c and incorporate the related interrupt functionality into your custom driver.

As a simpler alternative, you could also do the following:

1. Use the spidev.c driver discussed earlier as-is. There are device tree examples readily available that you can just leverage, see the end of this page here: https://software-dl.ti.com/processor-sdk-linux/esd/AM62X/09_02_01_10/exports/docs/linux/Foundational_Components/Kernel/Kernel_Drivers/SPI.html
   
   
2. Use a gpiod-based library approach (https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/about/) to capture GPIO interrupts and propagate them to userspace. There's actually an E2E thread that was just posted on this topic, so you can just follow this along for a solution: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1378524/tmds64evm-gpio-falling-edge-interrupt-configuration

Regards, Andreas