slave_mem_i2c_burst.c

/*
 * Copyright (c) 2021 Valentin Milea <valentin.milea@gmail.com>
 * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <hardware/i2c.h>
#include <pico/i2c_slave.h>
#include <pico/stdlib.h>
#include <stdio.h>
#include <string.h>

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

#ifdef i2c_default
// 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;

// The slave implements a 256 byte memory. To write a series of bytes, the master first
// writes the memory address, followed by the data. The address is automatically incremented
// for each byte transferred, looping back to 0 upon reaching the end. Reading is done
// sequentially from the current memory address.
static struct
{
    uint8_t mem[256];
    uint8_t mem_address;
    bool mem_address_written;
} context;

// 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) {
    switch (event) {
    case I2C_SLAVE_RECEIVE: // master has written some data
        if (!context.mem_address_written) {
            // writes always start with the memory address
            uint8_t by = i2c_read_byte_raw(i2c);
            context.mem_address = by;
            context.mem_address_written = true;
        } else {
            // save into memory
            uint8_t by = i2c_read_byte_raw(i2c);
            context.mem[context.mem_address] = by;
            context.mem_address++;
        }
        break;
    case I2C_SLAVE_REQUEST: // master is requesting data
        // load from memory
        i2c_write_byte_raw(i2c, context.mem[context.mem_address]);
        context.mem_address++;
        break;
    case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
        context.mem_address_written = false;
        break;
    default:
        break;
    }
}

static void setup_slave() {
    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 run_master() {
    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);

    for (uint8_t mem_address = 0;; mem_address = (mem_address + 32) % 256) {
        char msg[32];
        snprintf(msg, sizeof(msg), "Hello, I2C slave! - 0x%02X", mem_address);
        uint8_t msg_len = strlen(msg);

        uint8_t buf[32];
        buf[0] = mem_address;
        memcpy(buf + 1, msg, msg_len);
        // write message at mem_address
        printf("Write at 0x%02X: '%s'\n", mem_address, msg);
        for(int i = 0; i < (1 + msg_len); i++) {
            int count;
            if (i < (1 + msg_len - 1)) {
                count = i2c_write_burst_blocking(i2c1, I2C_SLAVE_ADDRESS, &buf[i], 1);
                sleep_ms(1); // gratuitous sleep for demonstration purposes - don't do this in real code!
            } else if (i == (1 + msg_len - 1)) {
                count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, &buf[i], 1, false);
            }
            if (count != 1) {
                puts("Couldn't write to slave, please check your wiring!");
                return;
            }
        }

        // seek to mem_address
        int count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, 1, true);
        hard_assert(count == 1);

        // partial read
        for(int i = 0; i < msg_len; i++) {
            if (count < (msg_len - 1)) {
                count = i2c_read_burst_blocking(i2c1, I2C_SLAVE_ADDRESS, buf + i, 1);
                sleep_ms(1); // gratuitous sleep for demonstration purposes - don't do this in real code!
            } else {
                count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, buf + i, 1, false);
            }
            hard_assert(count == 1);
        }
        buf[msg_len] = '\0';
        printf("Read  at 0x%02X: '%s'\n", mem_address, buf);
        hard_assert(memcmp(buf, msg, msg_len) == 0);

        puts("");
        sleep_ms(2000);
    }
}
#endif

int main() {
    stdio_init_all();
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c / slave_mem_i2c example requires a board with I2C pins
    puts("Default I2C pins were not defined");
    return 0;
#else
    puts("\nI2C slave example");

    setup_slave();
    run_master();
#endif
}