"""
Driver for accelerometer on STM32F4 Discover board.

Assumes it's a LIS302DL MEMS device.
Sets accelerometer range at +-2g.
Returns list containing X,Y,Z axis acceleration values in 'g' units (9.8m/s^2).

See:
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/Components/lis302dl/lis302dl.h
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/Components/lis302dl/lis302dl.c
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/STM32F4-Discovery/stm32f4_discovery.c
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/STM32F4-Discovery/stm32f4_discovery.h
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/STM32F4-Discovery/stm32f4_discovery_accelerometer.c
    STM32Cube_FW_F4_V1.1.0/Drivers/BSP/STM32F4-Discovery/stm32f4_discovery_accelerometer.h
    STM32Cube_FW_F4_V1.1.0/Projects/STM32F4-Discovery/Demonstrations/Src/main.c
"""

from pyb import Pin
from pyb import SPI

READWRITE_CMD = const(0x80) 
MULTIPLEBYTE_CMD = const(0x40)
LIS302DL_WHO_AM_I_ADDR = const(0x0f)
LIS302DL_WHO_AM_I_VAL = const(0x3b)
LIS302DL_CTRL_REG1_ADDR = const(0x20)
LIS302DL_OUT_X = const(0x29)
# Configuration for 100Hz sampling rate, +-2g range
LIS302DL_CONF = 0b01000111

def signed8(x):
    if x & 0x80:
        return x - 256
    else:
        return x

class STAccel:
    def __init__(self):
        self.cs_pin = Pin('PE3', Pin.OUT_PP, Pin.PULL_NONE)
        self.cs_pin.high()
        self.spi = SPI(1, SPI.MASTER, baudrate=328125, polarity=0, phase=1, bits=8)
        self.wr(LIS302DL_CTRL_REG1_ADDR, bytearray([LIS302DL_CONF]))
        if(self.read_id()[0] != LIS302DL_WHO_AM_I_VAL):
            raise Exception('LIS302DL accelerometer not present')

    def rd(self, addr, nbytes):
        if nbytes > 1:
            addr |= READWRITE_CMD | MULTIPLEBYTE_CMD
        else:
            addr |= READWRITE_CMD
        self.cs_pin.low()
        self.spi.send(addr)
        buf = self.spi.send_recv(bytearray(nbytes * [0])) # read data, MSB first
        self.cs_pin.high()
        return buf

    def wr(self, addr, buf):
        if len(buf) > 1:
            addr |= MULTIPLEBYTE_CMD
        self.cs_pin.low()
        self.spi.send(addr)
        for b in buf:
            self.spi.send(b)
        self.cs_pin.high()

    def read_id(self):
        return self.rd(LIS302DL_WHO_AM_I_ADDR, 1)

    def get_xyz(self):
        val = self.rd(LIS302DL_OUT_X, 5)
        x = signed8(val[0]) * 18.0 / 1000
        y = signed8(val[2]) * 18.0 / 1000
        z = signed8(val[4]) * 18.0 / 1000
        return [x, y, z]