accel.c

/* lab4/accel.c */
/* Copyright (c) 2020 J. M. Spivey */

#include "microbian.h"
#include "hardware.h"

/* Accelerometer */

/* Different revisions of the micro:bit have different accelerometer
chips: a MMA8653FC on the first revision of V1, and a LSM303AGR on the
second revision of V1 and on V2 (also including the magnetometer in
the same chip).  Each chip has its own I2C address and its own
internal structure. */

#define ACC1 0x1d               /* I2C address of accelerometer */
#define ACC1_CTRL_REG1 0x2a     /* Control register */
#define ACC1_X_DATA 0x01        /* Acceleration data */

#define ACC2 0x19               /* I2C address of mk1.5 accelerometer */
#define ACC2_CTRL_REG1 0x20     /* Control register */
#define ACC2_OUT 0x28           /* Acceleration data (different format) */

static int accel = 0;           /* 1 or 2 to select a chip type */

/* acc1_read -- read acceleration data (v1) */
static void acc1_read(int *x, int *y, int *z)
{
    signed char buf[3];
    i2c_read_bytes(I2C_INTERNAL, ACC1, ACC1_X_DATA, (byte *) buf, 3);
    *x = -buf[0]; *y = buf[1]; *z = -buf[2];
}

/* acc2_read -- read acceleration data (v2) */
static void acc2_read(int *x, int *y, int *z)
{
    signed char buf[6];
    i2c_read_bytes(I2C_INTERNAL, ACC2, ACC2_OUT|0x80, (byte *) buf, 6);
    *x = buf[1]; *y = buf[3]; *z = -buf[5];
}

/* accel_start -- initialise accelerometer */
void accel_start(void)
{
    /* Find chip and set to 50Hz, 8 bit, Active */
    if (i2c_probe(I2C_INTERNAL, ACC1) == OK) {
        i2c_write_reg(I2C_INTERNAL, ACC1, ACC1_CTRL_REG1, 0x23);
        accel = 1;
    } else if (i2c_probe(I2C_INTERNAL, ACC2) == OK) {
        i2c_write_reg(I2C_INTERNAL, ACC2, ACC2_CTRL_REG1, 0x4f);
        accel = 2;
    } else {
        panic("Can't find accelerometer");
    }
}

/* accel_reading -- obtain accelerometer reading */
void accel_reading(int *x, int *y, int *z)
{
    switch (accel) {
    case 1:
        acc1_read(x, y, z);
        break;
    case 2:
        acc2_read(x, y, z);
        break;
    default:
        panic("Unknown accelerometer");
    }
}