why SPI easyDMA maxcount is limited to 256byte?

[Haruki Kawakami]

Hi,

In the nrf52.h, SPIM_RXD_Type is defined as below.

typedef struct {
  __IO uint32_t  PTR;/*!< Data pointer */
  __IO uint32_t  MAXCNT;/*!< Maximum number of bytes in receive buffer*/
  __I  uint32_t  AMOUNT;/*!< Number of bytes transferred in the last transaction*/
  __IO uint32_t  LIST;/*!< EasyDMA list type */
} SPIM_RXD_Type;

So, NRF_SPIM0->RXD.MAXCNT can be set more than 256 and up to 2^32-1.

Why nrf_drv_spi_transfer's length argument is limited to 8bit?

I can't use ppi with SPI easyDMA (list feature), because SPI module is used by 3 sensors.

Thank you.

[Sigurd]

Hi,

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

[Wojtek]

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

[Haruki Kawakami]

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

[Haruki Kawakami]

you mean,

1. connect spi transfer ENDRX event and timer count task using ppi.

2. connect timer compare event(triggered when counter reaches array list size)and spi stop task using ppi.

3. enable timer compare event IRQ and in the IRQ set spi_xfer_done true.

4. 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.

[Wojtek]

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.