SPI delay betwen byte

[Fb62]

Hello,

I have a problem with the SPI of the nRF52DK 52832, and Zephyr 1.6.1. I have to transmit 10 frames of 5760 bytes each to the TFT display with the ST7789 driver.

The transmission is successful but I measured a delay between one byte and the next of almost 2 uS,

which makes the writing of the frame perceptible. Is it possible to reduce this delay between bytes?

The SPI is thus initialized.

static const struct spi_config spi_cfg = {
.operation =SPI_OP_MODE_MASTER|SPI_WORD_SET(8)| SPI_TRANSFER_MSB | SPI_MODE_CPOL | SPI_MODE_CPHA,
.frequency = 8000000,
.slave =0,

};

and I use spi_write to send the frame:

uint16_t fBuffer[5760];

void sendfBuffer(int y)
{

struct spi_buf tx_buf = {
.buf = fBuffer,
.len = sizeof(fBuffer)
};

struct spi_buf_set tx = {
.buffers = &tx_buf,
.count = 1
};

startWrite();// cs low
setAddrWindow(0, y,240,24); // set the position of the frame 
spi_write(spi2_dev,&spi_cfg,&tx); // send buffer to display
endWrite();//cs high

}

Best regards

[Sigurd]

Hi,

uint16_t fBuffer[5760];

 Try using uint8_t instead.

[Fb62]

Hi it's the same delay of 2 uS .

What is the default cpu clock, it's possible increase it?

regards

Fausto

[Sigurd]

Fb62 said:

it's the same delay of 2 uS .

 How are you measuring this?

I tried reprodcuing it, but I'm seeing 1 µs on the logic analzyer:

[Fb62]

HI,  Sigurd,

unfortunately my nRF52-DK doesn't work anymore,

I think the PCA10040 is broken (power and clock is ok, but the pc doesn't recognize it anymore).

So I can't send you a photo of the spi transmission with the delays.

I bought a new nRF52-DK, from mouser, as soon as I get it I redo the test and send a photo.

What I see on my analyzer doesn't look like your measurement at all, where the clock is continuous.

In my transmission the clock stops after 8 bits, pausing for 2 microseconds, to resume for the transmission of the next byte, and so on.

I am using nRF52832 with Zephyr 1.6.1 whit Segger, what version did you use to do this test?

Thank you, 

Fausto

[Fb62]

SDK 1.6.1

[Fb62]

Hi Sigurd,

it is possible to have the test code you did, so when I get the new DK, I also try your code.

Thanks

Fausto

[Sigurd]

Hi Fausto,

Fb62 said:

unfortunately my nRF52-DK doesn't work anymore,

 This post might be helpful in recovering it: https://devzone.nordicsemi.com/f/nordic-q-a/24592/my-nrf52-nrf51-dk-kit-doesn-t-work/

 

Fb62 said:

it is possible to have the test code you did, so when I get the new DK, I also try your code.

 Attachment: 8053.spi_test.rar

PS: You might have been affected by this nRF52832 errata: https://infocenter.nordicsemi.com/index.jsp?topic=%2Ferrata_nRF52832_Rev2%2FERR%2FnRF52832%2FRev2%2Flatest%2Fanomaly_832_58.html

[Fb62]

Hi Sigurd,

thanks a lot for your help, I have reprogrammed the DK and now works.

I Have tested your example and work perfect and I have noted tha the buffer of SPI is 255 bytes.

I found why in my application  i see a pause 2 uS every byte , because in overlay file i have this code

&spi2 {
compatible = "nordic,nrf-spi";
status = "okay";
label ="SPI_2";
sck-pin = <2>;
mosi-pin = <3>;
miso-pin = <4>;
cs-gpios = <&gpio0 25 0>;
};

I have changed "nordic,nrf-spi" to "nordic,nrf-spim" and now work well.

Thanks

Fausto