SPIM EasyDMA - sending and reading one byte

RE: SPIM EasyDMA - sending and reading one byte

Wojtek — Wed, 27 Apr 2016 09:45:59 GMT

It is a bug in the chip project i think. It is described in errata

RE: SPIM EasyDMA - sending and reading one byte

kijemwoko — Wed, 27 Apr 2016 08:52:25 GMT

I looked after nrf_drv_spi_transfer() function. There is simple setting of DMA registers as in my write function. Btw. I know the data should be in RAM section (I made a test - I located the transmit DMA buffer in flash and no error occured).

Example provided below for reading one byte clocks 16bits of data:

eventClear(Event::END);
spi.TXD.PTR = reinterpret_cast<uint32_t>(&write);
spi.TXD.MAXCNT = 0;    
spi.RXD.PTR = reinterpret_cast<uint32_t>(&buffer); 
spi.RXD.MAXCNT = 1;
spi.ORC = 0;
taskTrigger(Task::START);

Pertaining to the datasheet above solution shouldn't be used because of 0 written to MAXCNT register. With ones in MAXCNT registers the situation is the same.

My most recent test shows that calling above function (with 1 in TX MAXCNT and RX MAXCNT) clocks alternately 8bits and 16bits (16bits just after enabling SPIM) :) How to force the peripheral to send only 8bit?

RE: SPIM EasyDMA - sending and reading one byte

Kenneth — Wed, 27 Apr 2016 07:57:34 GMT

Hi, I can confirm that if I use \examples\peripheral\spi\ in the nRF5 SDK v11, I can read and write only 8 bit by setting m_length = 1 when calling nrf_drv_spi_transfer(). This example use the nrf_drv_spi configured with easyDMA, maybe you can use it as reference.

There is however an Errata 58 : SPIM: An additional byte is clocked out when RXD.MAXCNT = 1 that you should check out.