stmhal: Working STM32F4DISC accelerometer, via Python script.

Thanks to David Siorpaes.

stmhal/boards/STM32F4DISC/staccel.py

@@ -2,8 +2,8 @@
 Driver for accelerometer on STM32F4 Discover board.
 
 Assumes it's a LIS302DL MEMS device.
-
-Not currently working.
+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
@@ -22,12 +22,22 @@ READWRITE_CMD = const(0x80)
 MULTIPLEBYTE_CMD = const(0x40)
 LIS302DL_WHO_AM_I_ADDR = const(0x0f)
 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]))
 
     def rd(self, addr, nbytes):
         if nbytes > 1:
@@ -52,5 +62,9 @@ class STAccel:
     def read_id(self):
         return self.rd(LIS302DL_WHO_AM_I_ADDR, 1)
 
-    def init(self, init_param):
-        self.wr(LIS302DL_CTRL_REG1_ADDR, bytearray([init_param]))
+    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]