there are 10us delay between nrf5340 spi write and read sequence

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Fri, 05 Mar 2021 14:38:50 GMT

Check out the note given here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/ug_nrf5340.html#working-with-nrf53-series

"See the nRF Connect SDK v1.4.0 documentation for the last release supporting the nRF5340 PDK."

Check out NCS v1.4.0 for nrf5340 pdk

Best regards,

Simon

RE: there are 10us delay between nrf5340 spi write and read sequence

sunnyyang — Fri, 05 Mar 2021 14:21:55 GMT

hi simon,

I use the nrfx SPI API but error occur in code running.What causes this error？My board type is nrf5340pdk. The same code running in 5340dk is normal.What's the difference between the two boards？

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Thu, 04 Mar 2021 16:39:02 GMT

You may check out this case https://devzone.nordicsemi.com/f/nordic-q-a/66488/using-spi-with-ppi-in-zephyr/272139#272139 where a colleague has attached a sample where the nrfx SPI API is used directly

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Mon, 01 Mar 2021 18:40:32 GMT

I did some investigation today. What I did was to read the PARTID register of the adxl362 sensor using the nRF5340. That requires a write followed by a read, like you described. It took about 9.14 us between the two transactions. I used the following code to perform the write/read at once:

static int adxl362_read_reg(uint8_t reg_addr, void *data, size_t length)
{
	uint8_t access[2] = { ADXL362_READ_REG, reg_addr };
	const struct spi_buf buf[2] = {
		{
			.buf = access,
			.len = 2
		},
		{
			.buf = data,
			.len = length
		}
	};
	struct spi_buf_set tx = {
		.buffers = buf,
	};

	const struct spi_buf_set rx = {
			.buffers = buf,
			.count = 2
		};

	tx.count = 1;

	return spi_transceive(spi_dev, &spi_cfg, &tx, &rx);
}

I triggered a GPIO when NRF_SPIM_EVENT_END happened (called END_EVENT in the image):

https://github.com/nrfconnect/sdk-hal_nordic/blob/8f013ea950f41bf69b18bf688bfb0dd80a3fdc44/nrfx/drivers/src/nrfx_spim.c#L768

I also triggered a GPIO when the NRF_SPIM_TASK_START was triggered (called START_TASK in the image)

https://github.com/nrfconnect/sdk-hal_nordic/blob/8f013ea950f41bf69b18bf688bfb0dd80a3fdc44/nrfx/drivers/src/nrfx_spim.c#L603

Here is the result:

As you can see, there is some delay betwwen the task NRF_SPIM_TASK_START and the begining of the transaction. This task is sent direcly to the spi, so the this delay is due to the SPI peripheral.

You can also see that there is a delay between the first transaction and the first NRF_SPIM_EVENT_END event received, that delay is also due to the SPI peripheral, since it will generate this event after the ENDRX and ENDTX events are generated, read more about it here: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf5340%2Fspim.html&cp=3_0_0_6_29_0&anchor=concept_lhv_fx2_wr

The delay between the first NRF_SPIM_EVENT_END event and the second NRF_SPIM_TASK_START is due to the CPU, it has a handler that receives the end event before starting the next transaction.

I guess there is not much to do with the delay caused by the SPI. However to decrease the time caused by the CPU, you could use the NRFX API directly. I guess that will reduce the time, since there are many abstraction layers and overhead in Zephyr that may increase the time.

Best regards,

Simon

RE: there are 10us delay between nrf5340 spi write and read sequence

sunnyyang — Mon, 01 Mar 2021 14:15:32 GMT

hi simon,

Is there any progress on this issue?

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Thu, 25 Feb 2021 14:56:11 GMT

I tested this out myself and got about the same result as you. I tried to write to a register of an adxl362 and then read it, and checked the lines on a logic analyzer.

I guess around 10us is what the CPU needs in order to execute the necessary instructions in order to set up and execute and spi read.

I'll take a closer look at it tomorrow and try to give you a more detailed answer.

RE: there are 10us delay between nrf5340 spi write and read sequence

sunnyyang — Thu, 25 Feb 2021 13:48:44 GMT

hi simon，

Please could you advise me what I should do?

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Tue, 23 Feb 2021 15:40:33 GMT

Ah, okay. I understand. I'll look into it tomorrow.

Best regards,

Simon

RE: there are 10us delay between nrf5340 spi write and read sequence

sunnyyang — Tue, 23 Feb 2021 15:12:11 GMT

I want the clock to be continuous for read and write operations.Now The interval between write and read operations is 10us.

RE: there are 10us delay between nrf5340 spi write and read sequence

Simon — Tue, 23 Feb 2021 14:54:19 GMT

I'm not sure if I understand this question: "How can I make the write and read sequence continue?" Can you elaborate?