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I am using the pigpio C interface to drive an OLED, and cannot send transfers of over 128 bytes using the spi_write command. Apart from this spi_write works, as well as all other GPIO pin use for D/C and RES flags.

I can confirm this is not a hardware or OLED issue as I have a logic analyzer hooked up and increasing the transfer amount over 128 bytes results in nothing being sent, so it is likely a PIGPIO / SPIDEV / RPi issue.

Initialisation of the pigpio daemon:

initNewGPIO = pigpio_start(NULL, NULL); // Initialise pigpio

Opening SPI interface:

portNewWrite = spi_open(initNewGPIO, 0, 1000000, 0); // Channel, Baud, Flags

Regular call of the spi_write function (preceded by setting D/C flag and filling buffer with desired data):

spi_write(initNewGPIO, portNewWrite, data, count); // where data[] is a char* array of 8192 bytes, and count is a sizeof(data)

The previous initialisation and calls have no output on the SPI lines at all when sending more than 128 bytes at a time. The initialisation happens, followed by no activity on the MOSI line. Sending 128 bytes outputs normally:

WORKS CORRECTLY

spi_write(initNewGPIO, portNewWrite, data, 128); // data[] is a char* array of 128 bytes

NO SPI OUTPUT

spi_write(initNewGPIO, portNewWrite, data, 8192); // data[] is a char* array of 8192 bytes

(Logic Analyzer output)

I am relatively new to pigpio and spi-dev and would appreciate any troubleshooting tips to be able to better understand what's going on here. Is this an issue with my baud rate, or the SPI mode that I am using?

Please let me know if I should provide additional information to make the issue more clear.

Thanks, H

EDIT 1: A more complete code example for context, showing the SPI write function which is used to send the framebuffer to the display.

// We're using Braodcom pin numbers
unsigned int BUSY = 24;
unsigned int RESET = 25;

char *fb = (char *) calloc(8192, sizeof(char));

int status, portRead, initGPIO;

void fillBuffer()
{
    for (int n = 0; n < sizeof(fb); n++){
      fb[n] = 0xF;
    }
}

void initPort() 
{
    initGPIO = pigpio_start(NULL, NULL); // Initialise pigpio
    if (initGPIO < 0) 
    {
        printf("Failed to initialise GPIO for OLED... [pigpio]\n");
        printf("PIGPIO error code: %d\n", initGPIO);
    } 
    else
    { 
        printf("Initialised GPIO for OLED [pigpio]\n");
    }

    set_mode(initGPIO, RESET, PI_OUTPUT); // SET 25 (RESET) to input
    gpio_write(initGPIO, RESET, 1); // Raise RESET

    portRead = spi_open(initGPIO, 0, 1000000, 0); // Channel, Baud, Flags
    
}

void writePort(char data[], uint8_t count) 
{
    status = spi_write(initGPIO, portRead, data, count);

    if (status != count) 
    {
        printf("Status: %d", status); // print simultaneous SPI transfer result
    }
}

int main(void)
{
    initPort();
    fillBuffer();
    writePort(fb, sizeof(fb));

    return 0;
}
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  • Could you add a small but complete program which can be run to show the problem?
    – joan
    Nov 29, 2022 at 13:45
  • Sorry about the delay, I have added a simplified version of my code to the post.
    – hal
    Nov 30, 2022 at 11:01

1 Answer 1

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The code does not compile.

In future please provide a complete example with build instructions.

One problem, perhaps the problem, is the count is constrained to fit in a uint8_t (maximum 255). Perhaps change that to a uint.

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