why SPI easyDMA maxcount is limited to 256byte?

RE: why SPI easyDMA maxcount is limited to 256byte?

Wojtek — Thu, 16 Feb 2017 14:55:43 GMT

Of course it is. You can just manually start each transfer. But I really see no reason why would You want to do it.

RE: why SPI easyDMA maxcount is limited to 256byte?

Haruki Kawakami — Thu, 16 Feb 2017 14:05:07 GMT

I want to use spi list feature without ppi. Is that possible?

Because I have to use the same spi module for OLED, SPI flash and accelerometer with FIFO, spi ppi that I have to set spi tx and rx buffer in advance can't be used.

RE: why SPI easyDMA maxcount is limited to 256byte?

Wojtek — Thu, 16 Feb 2017 12:26:20 GMT

I don't know what exactly you want achieve, but I would do something like this:

SPI END event triggering TIMER COUNT task
timer CC event IRQ moving the SPI data pointer

I am not using spi drv in my apps - direct manipulation in registers is more clear for me.

RE: why SPI easyDMA maxcount is limited to 256byte?

Haruki Kawakami — Thu, 16 Feb 2017 11:45:05 GMT

you mean,

connect spi transfer ENDRX event and timer count task using ppi.
connect timer compare event(triggered when counter reaches array list size)and spi stop task using ppi.
enable timer compare event IRQ and in the IRQ set spi_xfer_done true.
use nrf_drv_spi_transfer() with NRF_DRV_SPI_FLAG_TX_POSTINC, NRF_DRV_SPI_FLAG_RX_POSTINC, NRF_DRV_SPI_FLAG_NO_XFER_EVT_HANDLER, and NRF_DRV_SPI_FLAG_REPEATED_XFER flag (= without NRF_DRV_SPI_FLAG_HOLD_XFER flag).

is this true?

If not, because I couldn't have found any sample code using spi list mode, can you show me the sample code or procedure?

Thank you.

RE: why SPI easyDMA maxcount is limited to 256byte?

Haruki Kawakami — Thu, 16 Feb 2017 11:12:38 GMT

Thank you! However, why don't you utilize full 32 bit? You reserve 32 bit for NRF_SPIM0->RXD.MAXCNT by the document.

RE: why SPI easyDMA maxcount is limited to 256byte?

Wojtek — Tue, 14 Feb 2017 15:29:02 GMT

If there is a problem with using CS between array lists, you always can use gpiote toggling triggered by timers/counters/finished transfers etc, so you can achieve long transmissions

RE: why SPI easyDMA maxcount is limited to 256byte?

Sigurd — Tue, 14 Feb 2017 14:32:58 GMT

Hi,

NRF_SPIM0->RXD.MAXCNT is 8 bit, and not 32 bit. See the register here, and this thread.