RP2040 SPI Chip Select delay time

Other Hardware 3rd Party Boards
1

Hi All!!

I'm using RP2040 pi pico on Arduino Mbed environment.
I hope to control 8 SPI devices by using single SPI bus and 8 Chip Select gpio. The SPI related program is very simple like as bellow.

digitalWrite(dac[ic], LOW); // DAC CS
SPI.transfer(buff, len);
digitalWrite(dac[ic], HIGH);

The time between Chip Select and first SPI_CLK is too longer than my expectation (less than 1us) and I'm looking for the solution but did not find yet. I also changed digitalWrite() function to gpio_clr_mask() to reduce delay time but this is not key impact factor.

Pls advise for me.

tek00004
tek000041024×768 53.9 KB

2

Check the datasheet, if the SPI is working, maybe it's the problem in the GPIO, when it operates the CS pin, there is usually a time to write to the pins, try looking for fast writing, usually have to directly manipulate the microcontroller registers that control the pins.

3

Thanks for your comment and sharing datasheet. I already try direct gpio pin access for chip select and this only reduce total 500ns delay time. There are big delay between CS to CLK around 5 to 7 us.

4

Try to operate all communication directly too, libraries usually add delays to make the function more adaptable.

1 Like
5

Hi! All!

I solved this problem by using another SPI library, PicoSPI.

void DAC_Write(int ic, int ch, uint8_t *buff, int len) {
  uint32_t mask;

  mask = 0x01 << dac[ic];
  buff[0] = (buff[0] + ch) & 0xff;
  //digitalWrite(dac[ic], LOW);   // DAC CS
  gpio_clr_mask(mask);            // DAC CS
  PicoSPI0.beginTransaction() ;
  for (int i = 0; i < len; i++)
    PicoSPI0.transfer (buff[i]) ;  
  PicoSPI0.endTransaction() ;
  //SPI.transfer(buff, len);
  //digitalWrite(dac[ic], HIGH);
  gpio_set_mask(mask);
}

Finally I got the more faster SPI access result like as follow.
Thanks to everybody who support me.

tek00005
tek000051024×768 72.3 KB

6

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