scan_i2c.c

// Copyright (c) 2022 Useful Sensors Inc.
// SPDX-License-Identifier: Apache-2.0
//
// Scans the I2C bus and shows what addresses are found.
// This can be helpful if you're trying to debug connection problems with your
// sensor.

#include <stdio.h>
#include <string.h>

#include "pico/stdlib.h"
#include "pico/binary_info.h"

#include "hardware/i2c.h"

// Speed of the I2C bus. The sensor supports many rates but 400KHz works.
const int32_t I2C_BAUD_RATE = (400 * 1000);

// I2C reserves some addresses for special purposes. We exclude these from the scan.
// These are any addresses of the form 000 0xxx or 111 1xxx
bool reserved_addr(uint8_t addr) {
    return (addr & 0x78) == 0 || (addr & 0x78) == 0x78;
}

// Call this function from the main loop below to see what peripherals are
// available on the I2C bus, if you're having problems communicating with the
// person sensor.
void scan_i2c_bus() {
  for (int addr = 0; addr < (1 << 7); ++addr) {
    if (addr % 16 == 0) {
      printf("%02x ", addr);
    }

    // Perform a 1-byte dummy read from the probe address. If a peripheral
    // acknowledges this address, the function returns the number of bytes
    // transferred. If the address byte is ignored, the function returns -1.

    // Skip over any reserved addresses.
    int ret;
    uint8_t rxdata;
    if (reserved_addr(addr)) {
      ret = PICO_ERROR_GENERIC;
    } else {
      ret = i2c_read_blocking(i2c_default, addr, &rxdata, 1, false);
    }
    printf(ret < 0 ? "." : "@");
    printf(addr % 16 == 15 ? "\n" : "  ");
  }
  printf("Done.\n");
}

int main() {
    stdio_init_all();

    printf("Setting up i2c\n");

    // Use I2C0 on the default SDA and SCL pins (6, 7 on a Pico).
    i2c_init(i2c_default, I2C_BAUD_RATE);
    gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
    gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);
    // Make the I2C pins available to picotool.
    bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, 
      PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));

    printf("Setup done for i2c\n");

    while (1) {
      // Keep scanning the bus every second.
      scan_i2c_bus();
      sleep_ms(1000);
    }

    return 0;
}