topic Implementing always-ready SPI slave with S32K and FreeRTOS in S32K

Implementing always-ready SPI slave with S32K and FreeRTOS

yfliu — Tue, 03 Aug 2021 06:04:16 GMT

Dear community members,

I am wondering how we can implement an always-ready SPI slave with S32K14x MCU and FreeRTOS?

By "always-ready" means that whenever the SPI master starts a duplex transfer by toggling the CS line, the MCU can respond immediately with data in an outgoing queue.

I am considering to have an ISR triggered by the CS line, within the ISR we initiate a SPI slave xfer using SPI device or PAL driver. But I am unsure if the ISR can respond fast enough? Should we ask the SPI master side to wait a while before sending the SCLK signals after toggleing the CS line?

If this works in general, what details should we watch (e.g. ISR priority etc)?

Regards,

Re: Implementing always-ready SPI slave with S32K and FreeRTOS

danielmartynek — Wed, 04 Aug 2021 11:37:06 GMT

Hi @yfliu,

Please refer to the description of the transmit FIFO in the Slave mode:

I think the best solution is to fill the transmit FIFO whenever the number of words in the FIFO drop below a certain level.

Regards,

Daniel

Re: Implementing always-ready SPI slave with S32K and FreeRTOS

yfliu — Fri, 13 Aug 2021 03:30:22 GMT

Hi @danielmartynek

Thank you for the design idea and sorry for my late reply.

Do you think if I can acheive the above idea using SPI_PAL library? or I have to use low-level drivers library?

I am wondering if I can use `SPI_SlaveTransfer()` within the TDF ISR callback?

Regards,

Yanfeng

Re: Implementing always-ready SPI slave with S32K and FreeRTOS

danielmartynek — Mon, 16 Aug 2021 13:47:31 GMT

Hi Yanfeng,

Looking at the callbacks.h header file, there is no TDF callback event just the SPI_EVENT_END_TRANSFER.

Regards,

Daniel