example_slave_transmitter_blocking.c

/*
 * Copyright (c) 2022 Valentin Milea <valentin.milea@gmail.com>
 *
 * SPDX-License-Identifier: MIT
 */

#include <i2c_fifo.h>
#include <i2c_slave.h>
#include <pico/multicore.h> // add pico_multicore to target_link_libraries
#include <pico/stdlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_TRANSFER_SIZE (4 + 128)

static const uint I2C_SLAVE_ADDRESS = 0x17;
static const uint I2C_BAUDRATE = 100000; // 100 kHz

// For this example, we run both the master and slave from the same board.
// You'll need to wire pin GP4 to GP6 (SDA), and pin GP5 to GP7 (SCL).
static const uint I2C_SLAVE_SDA_PIN = PICO_DEFAULT_I2C_SDA_PIN; // 4
static const uint I2C_SLAVE_SCL_PIN = PICO_DEFAULT_I2C_SCL_PIN; // 5
static const uint I2C_MASTER_SDA_PIN = 6;
static const uint I2C_MASTER_SCL_PIN = 7;

static struct
{
    critical_section_t crit_sec;
    bool has_request;
} slave;

// Our handler is called from the I2C ISR, so it must complete quickly. Blocking calls /
// printing to stdio may interfere with interrupt handling.
static void i2c_slave_handler(i2c_inst_t *i2c, i2c_slave_event_t event) {
    critical_section_enter_blocking(&slave.crit_sec);
    switch (event) {
    case I2C_SLAVE_RECEIVE: // master has written some data
        break;
    case I2C_SLAVE_REQUEST: // master is requesting data
        slave.has_request = true;
        __sev(); // notify slave transmitter
        break;
    case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
        break;
    default:
        break;
    }
    critical_section_exit(&slave.crit_sec);
}

static void i2c_slave_transmit_blocking(i2c_inst_t *i2c, const uint8_t *src, size_t len) {
    critical_section_enter_blocking(&slave.crit_sec);
    // wait until master has requested data
    while (!slave.has_request) {
        critical_section_exit(&slave.crit_sec);
        __wfe();
        critical_section_enter_blocking(&slave.crit_sec);
    }
    // clear flag
    slave.has_request = false;

    i2c_write_raw_blocking(i2c, src, len);
    critical_section_exit(&slave.crit_sec);
}

static void setup_slave(void ) {
    critical_section_init(&slave.crit_sec);
    
    gpio_init(I2C_SLAVE_SDA_PIN);
    gpio_set_function(I2C_SLAVE_SDA_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(I2C_SLAVE_SDA_PIN);

    gpio_init(I2C_SLAVE_SCL_PIN);
    gpio_set_function(I2C_SLAVE_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(I2C_SLAVE_SCL_PIN);

    i2c_init(i2c0, I2C_BAUDRATE);
    // configure I2C0 for slave mode
    i2c_slave_init(i2c0, I2C_SLAVE_ADDRESS, &i2c_slave_handler);
}

static void master_thread() {
    gpio_init(I2C_MASTER_SDA_PIN);
    gpio_set_function(I2C_MASTER_SDA_PIN, GPIO_FUNC_I2C);
    // pull-ups are already active on slave side, this is just a fail-safe in case the wiring is faulty
    gpio_pull_up(I2C_MASTER_SDA_PIN);

    gpio_init(I2C_MASTER_SCL_PIN);
    gpio_set_function(I2C_MASTER_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(I2C_MASTER_SCL_PIN);

    i2c_init(i2c1, I2C_BAUDRATE);

    static uint32_t data[MAX_TRANSFER_SIZE / sizeof(uint32_t)];
    do {
        puts(" Read header...");
        size_t len = 0;
        int count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, (uint8_t*)&len, sizeof(uint32_t), true);
        if (count != sizeof(uint32_t)) {
            puts(" Couldn't read from slave, please check your wiring!");
            return;
        }
        printf("  len: %u\n", len);
        size_t payload_size = len * sizeof(uint32_t);
        hard_assert(payload_size <= MAX_TRANSFER_SIZE);
        puts(" Read payload...");
        count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, (uint8_t*)data, payload_size, false);
        hard_assert(count == payload_size);
        for (size_t i = 0; i < len; i++) {
            printf("  %u\n", (uint)data[i]);
        }
        puts("");

        sleep_ms(100);
    } while (true);
}

int main() {
    stdio_init_all();
    puts("\nI2C slave - transmit blocking");
    
    setup_slave();
    multicore_launch_core1(master_thread);

    size_t processed_data_len = MAX_TRANSFER_SIZE / sizeof(uint32_t) - 1;
    uint32_t *processed_data = malloc(processed_data_len * sizeof(uint32_t));
    uint32_t counter = 0;

    do {
        // prepare next data set
        for (size_t i = 0; i < processed_data_len; i++) {
            processed_data[i] = counter++;
        }
        // simulate processing lag; master tries to read immediately, but I2C bus will be
        // stalled until slave starts transmitting
        sleep_ms(1000);

        // transmit header
        i2c_slave_transmit_blocking(i2c0, (uint8_t*)&processed_data_len, sizeof(uint32_t));
        // transmit payload
        i2c_slave_transmit_blocking(i2c0, (uint8_t*)processed_data, processed_data_len * sizeof(uint32_t));
    } while (true);
}