AD5721R problem with SPI latency

RE: AD5721R problem with SPI latency

Kenneth — Mon, 08 Apr 2019 09:30:19 GMT

Hi,

I suspect this works "better" because you don't have any interrupt delays. If you are using the driver in blocking mode (e.g. no callback handler registered when init spi driver), then this should be a safe usage.

Best regards,
Kenneth

RE: AD5721 problem with SPI speed

Niklas_H — Fri, 05 Apr 2019 12:06:05 GMT

I resolved the issue by using the spi master driver instance in blocking mode.

nrf_drv_spi_init(&spi, &spi_config, NULL,NULL);

And by commenting out the while loop with WFE() in the write function of the DAC.

void ad5721r_write( uint8_t reg_addr_cmd, uint16_t reg_data)
{
	uint8_t data[3];
	ret_code_t ret;

	data[0] = reg_addr_cmd; 
	data[1] = (reg_data & 0xFF00) >> 8; 
	data[2] = (reg_data & 0x00FF) >> 0; 

    memset(m_rx_buf, 0, m_length);
	spi_xfer_done = 0;
	nrf_drv_spi_transfer(&spi, data, 3, m_rx_buf, 0);
//	while (!spi_xfer_done)
//		{
//			__WFE();
//		}
}

I guess this will make it more dangerous to call it too often without checking the status of the transfer? Could this cause bigger issues when using BLE softdevice or other interrupts?

So far I had no problem running the DAC at 24 KHz and higher.

RE: AD5721 problem with SPI speed

Niklas_H — Thu, 04 Apr 2019 08:36:32 GMT

Thanks for the quick reply.

I checked, the spi driver is using EasyDMA. The application so far is pretty bare bone, no BLE softdevice or other interrupts are enabled. But I plan on using Bluetooth in the future.

The timer handler works fine to toggle a specific pin. Once the SPI handler is running the pin toggle also differs in duration. I’m starting to wonder if the DAC is limiting the frequency output.

I won’t be able to use the nrf58240 for my project. But good to know for future applications.

RE: AD5721 problem with SPI speed

Kenneth — Tue, 02 Apr 2019 19:30:18 GMT

I think the best option is to get yourself an nRF52840-DK instead, this chip have a new SPIM3 module with hardware SYNC (called CSN here) pin and faster clock speed:
http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52840.ps/spim.html?cp=2_0_0_5_24

If you want to continue investigate a bit the nRF52832 I would likely have tried to look at your interrupt priorities, and for instance toggle a specific pin while timer handler is executing and a different pin when spi handler is running, to check the order of the interrupts or the duration differs also here.

Make sure to check if the spi driver is using EasyDMA by looking at the sdk_config.h file, e.g.:

#ifndef SPI0_USE_EASY_DMA
#define SPI0_USE_EASY_DMA 1
#endif

Is the BLE softdevice enabled in your application? and/or other interrupts?