General • SPI master CSN question

Code:

#include <stdio.h>#include "pico/stdlib.h"#include "pico/binary_info.h"#include "hardware/spi.h"#define BUF_LEN         0x100#define PICO_DEFAULT_SPI_RX_PIN 0   // MOSI from master → receive on slave#define PICO_DEFAULT_SPI_SCK_PIN 2  // SPI clock#define PICO_DEFAULT_SPI_TX_PIN 3   // MISO to master#define PICO_DEFAULT_SPI_CSN_PIN 1  // Chip select (manual toggle)#define BAUD_RATE 115200int main() {    // Enable UART for printing    stdio_init_all();#if !defined(spi_default) || !defined(PICO_DEFAULT_SPI_SCK_PIN) || \    !defined(PICO_DEFAULT_SPI_TX_PIN) || !defined(PICO_DEFAULT_SPI_RX_PIN) || \    !defined(PICO_DEFAULT_SPI_CSN_PIN)#warning spi/spi_master example requires a board with SPI pins    puts("Default SPI pins were not defined");#else    // Enable SPI0 at 1 MHz and connect pins    spi_init(spi_default, 1000 * 1000); // 1 MHz    gpio_set_function(PICO_DEFAULT_SPI_RX_PIN, GPIO_FUNC_SPI);    gpio_set_function(PICO_DEFAULT_SPI_SCK_PIN, GPIO_FUNC_SPI);    gpio_set_function(PICO_DEFAULT_SPI_TX_PIN, GPIO_FUNC_SPI);    // CSN manually controlled    gpio_set_function(PICO_DEFAULT_SPI_CSN_PIN, GPIO_FUNC_SIO);    gpio_set_dir(PICO_DEFAULT_SPI_CSN_PIN, true);    gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 1); // idle high    // Make pins available to picotool    bi_decl(bi_4pins_with_func(PICO_DEFAULT_SPI_RX_PIN,                                PICO_DEFAULT_SPI_TX_PIN,                                PICO_DEFAULT_SPI_SCK_PIN,                                PICO_DEFAULT_SPI_CSN_PIN, GPIO_FUNC_SPI));    uint8_t out_buf[BUF_LEN], in_buf[BUF_LEN];    // Initialize output buffer    for (size_t i = 0; i < BUF_LEN; ++i) {        out_buf[i] = i;        in_buf[i] = 0;    }    while (1) {        // Pull CS low to start transfer        gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 0);        // SPI transfer (write & read)        spi_write_read_blocking(spi_default, out_buf, in_buf, BUF_LEN);        // Pull CS high to end transfer        gpio_put(PICO_DEFAULT_SPI_CSN_PIN, 1);        // Optional: print received data (for debugging)        // for (size_t i = 0; i < BUF_LEN; ++i) {        //     printf("%02X ", in_buf[i]);        // }        // printf("\n");        sleep_ms(10); // optional delay between packets    }#endif}

Code:

bool spi_irq_setup_init(void){    irq_set_enabled(SPI0_IRQ, false);    irq_set_exclusive_handler(SPI0_IRQ, irq_handler);    irq_set_priority(SPI0_IRQ, 0);    // Disable SPI before touching interrupt mask    // Clear any pending interrupts    hw_clear_bits(&spi_get_hw(spi0)->icr, SPI_SSPICR_RTIC_BITS| SPI_SSPICR_RORIC_BITS);    hw_clear_bits(&spi_get_hw(spi0)->imsc, SPI_SSPIMSC_BITS);    // Enable desired interrupt sources    hw_set_bits(&spi_get_hw(spi0)->imsc,                SPI_SSPIMSC_RTIM_BITS |                SPI_SSPIMSC_RXIM_BITS);    irq_set_enabled(SPI0_IRQ, true);    return irq_is_enabled(SPI0_IRQ);}