mpl3115a2_i2c.c

/**
 * Copyright (c) 2021 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "pico/binary_info.h"
#include "hardware/gpio.h"
#include "hardware/i2c.h"

/* Example code to talk to an MPL3115A2 altimeter sensor via I2C

   See accompanying documentation in README.adoc or the C++ SDK booklet.

   Connections on Raspberry Pi Pico board, other boards may vary.

   GPIO PICO_DEFAULT_I2C_SDA_PIN (On Pico this is 4 (pin 6)) -> SDA on MPL3115A2 board
   GPIO PICO_DEFAULT_I2C_SCK_PIN (On Pico this is 5 (pin 7)) -> SCL on MPL3115A2 board
   GPIO 16 -> INT1 on MPL3115A2 board
   3.3v (pin 36) -> VCC on MPL3115A2 board
   GND (pin 38)  -> GND on MPL3115A2 board
*/

// 7-bit address
#define ADDR 0x60
#define INT1_PIN _u(16)

// following definitions only valid for F_MODE > 0 (ie. if FIFO enabled)
#define MPL3115A2_F_DATA _u(0x01)
#define MPL3115A2_F_STATUS _u(0x00)
#define MPL3115A2_F_SETUP _u(0x0F)
#define MPL3115A2_INT_SOURCE _u(0x12)
#define MPL3115A2_CTRLREG1 _u(0x26)
#define MPL3115A2_CTRLREG2 _u(0x27)
#define MPL3115A2_CTRLREG3 _u(0x28)
#define MPL3115A2_CTRLREG4 _u(0x29)
#define MPL3115A2_CTRLREG5 _u(0x2A)
#define MPL3115A2_PT_DATA_CFG _u(0x13)
#define MPL3115A2_OFF_P _u(0x2B)
#define MPL3115A2_OFF_T _u(0x2C)
#define MPL3115A2_OFF_H _u(0x2D)

#define MPL3115A2_FIFO_DISABLED _u(0x00)
#define MPL3115A2_FIFO_STOP_ON_OVERFLOW _u(0x80)
#define MPL3115A2_FIFO_SIZE 32
#define MPL3115A2_DATA_BATCH_SIZE 5
#define MPL3115A2_ALTITUDE_NUM_REGS 3
#define MPL3115A2_ALTITUDE_INT_SIZE 20
#define MPL3115A2_TEMPERATURE_INT_SIZE 12
#define MPL3115A2_NUM_FRAC_BITS 4

#define PARAM_ASSERTIONS_ENABLE_I2C 1

volatile uint8_t fifo_data[MPL3115A2_FIFO_SIZE * MPL3115A2_DATA_BATCH_SIZE];
volatile bool has_new_data = false;

struct mpl3115a2_data_t {
    // Q8.4 fixed point
    float temperature;
    // Q16.4 fixed-point
    float altitude;
};

void copy_to_vbuf(uint8_t buf1[], volatile uint8_t buf2[], uint buflen) {
    for (size_t i = 0; i < buflen; i++) {
        buf2[i] = buf1[i];
    }
}

#ifdef i2c_default

void mpl3115a2_read_fifo(volatile uint8_t fifo_buf[]) {
    // drains the 160 byte FIFO
    uint8_t reg = MPL3115A2_F_DATA;
    uint8_t buf[MPL3115A2_FIFO_SIZE * MPL3115A2_DATA_BATCH_SIZE];
    i2c_write_blocking(i2c_default, ADDR, &reg, 1, true);
    // burst read 160 bytes from fifo
    i2c_read_blocking(i2c_default, ADDR, buf, MPL3115A2_FIFO_SIZE * MPL3115A2_DATA_BATCH_SIZE, false);
    copy_to_vbuf(buf, fifo_buf, MPL3115A2_FIFO_SIZE * MPL3115A2_DATA_BATCH_SIZE);
}

uint8_t mpl3115a2_read_reg(uint8_t reg) {
    uint8_t read;
    i2c_write_blocking(i2c_default, ADDR, &reg, 1, true); // keep control of bus
    i2c_read_blocking(i2c_default, ADDR, &read, 1, false);
    return read;
}

void mpl3115a2_init() {
    // set as altimeter with oversampling ratio of 128
    uint8_t buf[] = {MPL3115A2_CTRLREG1, 0xB8};
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // set data refresh every 2 seconds, 0 next bits as we're not using those interrupts
    buf[0] = MPL3115A2_CTRLREG2, buf[1] = 0x00;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // set both interrupts pins to active low and enable internal pullups
    buf[0] = MPL3115A2_CTRLREG3, buf[1] = 0x01;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // enable FIFO interrupt
    buf[0] = MPL3115A2_CTRLREG4, buf[1] = 0x40;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // tie FIFO interrupt to pin INT1
    buf[0] = MPL3115A2_CTRLREG5, buf[1] = 0x40;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // set p, t and h offsets here if needed
    // eg. 2's complement number: 0xFF subtracts 1 meter
    //buf[0] = MPL3115A2_OFF_H, buf[1] = 0xFF;
    //i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // do not accept more data on FIFO overflow
    buf[0] = MPL3115A2_F_SETUP, buf[1] = MPL3115A2_FIFO_STOP_ON_OVERFLOW;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);

    // set device active
    buf[0] = MPL3115A2_CTRLREG1, buf[1] = 0xB9;
    i2c_write_blocking(i2c_default, ADDR, buf, 2, false);
}

void gpio_callback(uint gpio, __unused uint32_t events) {
    // if we had enabled more than 2 interrupts on same pin, then we should read
    // INT_SOURCE reg to find out which interrupt triggered

    // we can filter by which GPIO was triggered
    if (gpio == INT1_PIN) {
        // FIFO overflow interrupt
        // watermark bits set to 0 in F_SETUP reg, so only possible event is an overflow
        // otherwise, we would read F_STATUS to confirm it was an overflow
        printf("FIFO overflow!\n");
        // drain the fifo
        mpl3115a2_read_fifo(fifo_data);
        // read status register to clear interrupt bit
        mpl3115a2_read_reg(MPL3115A2_F_STATUS);
        has_new_data = true;
    }
}

#endif

void mpl3115a2_convert_fifo_batch(uint8_t start, volatile uint8_t buf[], struct mpl3115a2_data_t *data) {
    // convert a batch of fifo data into temperature and altitude data

    // 3 altitude registers: MSB (8 bits), CSB (8 bits) and LSB (4 bits, starting from MSB)
    // first two are integer bits (2's complement) and LSB is fractional bits -> makes 20 bit signed integer
    int32_t h = (int32_t) buf[start] << 24;
    h |= (int32_t) buf[start + 1] << 16;
    h |= (int32_t) buf[start + 2] << 8;
    data->altitude = ((float)h) / 65536.f;

    // 2 temperature registers: MSB (8 bits) and LSB (4 bits, starting from MSB)
    // first 8 are integer bits with sign and LSB is fractional bits -> 12 bit signed integer
    int16_t t = (int16_t) buf[start + 3] << 8;
    t |= (int16_t) buf[start + 4];
    data->temperature = ((float)t) / 256.f;
}

int main() {
    stdio_init_all();
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c / mpl3115a2_i2c example requires a board with I2C pins
    puts("Default I2C pins were not defined");
    return 0;
#else
    printf("Hello, MPL3115A2. Waiting for something to interrupt me!...\n");

    // use default I2C0 at 400kHz, I2C is active low
    i2c_init(i2c_default, 400 * 1000);
    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);

    gpio_init(INT1_PIN);
    gpio_pull_up(INT1_PIN); // pull it up even more!

    // add program information for picotool
    bi_decl(bi_program_name("Example in the pico-examples library for the MPL3115A2 altimeter"));
    bi_decl(bi_1pin_with_name(16, "Interrupt pin 1"));
    bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));

    mpl3115a2_init();

    gpio_set_irq_enabled_with_callback(INT1_PIN, GPIO_IRQ_LEVEL_LOW, true, &gpio_callback);

    while (1) {
        // as interrupt data comes in, let's print the 32 sample average
        if (has_new_data) {
            float tsum = 0, hsum = 0;
            struct mpl3115a2_data_t data;
            for (int i = 0; i < MPL3115A2_FIFO_SIZE; i++) {
                mpl3115a2_convert_fifo_batch(i * MPL3115A2_DATA_BATCH_SIZE, fifo_data, &data);
                tsum += data.temperature;
                hsum += data.altitude;
            }
            printf("%d sample average -> t: %.4f C, h: %.4f m\n", MPL3115A2_FIFO_SIZE, tsum / MPL3115A2_FIFO_SIZE,
                   hsum / MPL3115A2_FIFO_SIZE);
            has_new_data = false;
        }
        sleep_ms(10);
    };

#endif
}