ESP32 Forum

Posted: **Mon Aug 07, 2023 8:53 am**

I have been experimenting with SPI;
Set and init for VSPI ok, then considering the code below:
(Ignoring that it will trigger watchdog in some seconds and etc.)
-Or working dedicated without interrupts enabled.

Code: [Select all] [Expand/Collapse]

// SPI configuration
#define PIN_NUM_MISO GPIO_NUM_19
#define PIN_NUM_MOSI GPIO_NUM_23
#define PIN_NUM_CLK  GPIO_NUM_18
#define PIN_NUM_CS   GPIO_NUM_5
 
    spi_bus_config_t bus_config;
    bus_config.miso_io_num = PIN_NUM_MISO;
    bus_config.mosi_io_num = PIN_NUM_MOSI;
    bus_config.sclk_io_num = PIN_NUM_CLK;
    bus_config.quadwp_io_num = -1;
    bus_config.quadhd_io_num = -1;
    bus_config.max_transfer_sz = 0;
 
    spi_device_interface_config_t dev_config;
    dev_config.clock_speed_hz = 1000000;  // Clock speed (1 MHz)
    dev_config.spics_io_num = PIN_NUM_CS;
    dev_config.queue_size = 1;
    dev_config.mode = 0;  // SPI mode 0
 
    spi_device_handle_t spi_handle;
 
    // Initialize the SPI bus
    esp_err_t ret;
    ret = spi_bus_initialize(VSPI_HOST, &bus_config, SPI_DMA_DISABLED);
    assert(ret == ESP_OK);
 
    // Attach the device to the SPI bus
    ret = spi_bus_add_device(VSPI_HOST, &dev_config, &spi_handle);
    assert(ret == ESP_OK);
 
    // Data to send
    spi_transaction_t trans;
    trans.flags = 0;
    trans.length = 64;  // Data length in bits
    trans.tx_buffer = data_to_send0;
 
    uint8_t data_to_send0[8] = { 0xFA, 0x5E, 0x01, 0xD0, 0xDA, 0xD0, 0xCA, 0xB0 };
    uint8_t data_to_send1[8] = { 0xFA, 0x5E, 0x02, 0xD0, 0xDA, 0xD0, 0xCA, 0xB1 };
 
    while (1)
    {
      trans.tx_buffer = data_to_send0;
      ret = spi_device_polling_transmit(spi_handle, &trans);
      //trans.tx_buffer = data_to_send1;
      //ret = spi_device_polling_transmit(spi_handle, &trans);
    }
 

GeSHi © Codebox Plus Extension

I have a couple of questions on this PoC/test code.
(This is not checking status of return, it previously was and it calls and works ok)

1-Even as it is above, with no scheduler interrupts, I checked in the logic analyzer to have a ~14 us delay between the data_to_send0 frames of data. I expect/need no delay in between calls, is something behind scenes that consumes the time after a transmit ends?

2-If I uncomment the second transmit, code breaks. Always. Immediately. So I cannot have double buffering for this? I tried also to let same references and refil a single data_to_send buffer, or have it source of data updated; is there some data lock or similar behind this, causing an access violation or whatever?

I do not want to reinvent the SPI and make a bit banging procedure for it to attend my need, what else could I do, in case someone have seen similar issues?
I need to feed a device near 1MHz limit of SPI functioning, few KB of data for a couple of seconds each time or so.

Thanks

PS. This runs in the second core, a single task, no interrupts. Disabled task watchdog.
PS2. Tried both using
trans.tx_buffer = data_to_send0;
and
trans.tx_buffer = &data_to_send0;
No change in results fir both working and not working cases.

Posted: **Mon Aug 07, 2023 12:44 pm**

First of all, please don't initialize your structs like that; make sure they're zeroed, e.g.

Code: Select all

    spi_device_interface_config_t dev_config={0};

Posted: **Mon Aug 07, 2023 1:21 pm**

[Edit] Thanks, this seems to have solved the issue.

I presume that, for the compiler, when the next example statement is made, the non mentioned fields are by default initialized to zero

Code: Select all

spi_bus_config_t buscfg={
        .miso_io_num = -1,
        .mosi_io_num = MOSI_PIN,
        .sclk_io_num = CLK_PIN,
        .quadwp_io_num = -1,
        .quadhd_io_num = -1,
        .max_transfer_sz = 32,
    };

Posted: **Tue Aug 08, 2023 1:47 am**

Yes, if you initialize it using that method, you'll zero-initialize unmentioned members.

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