From 8dd90cb3bcb8639313fc4ef7b330b7078dbda4f8 Mon Sep 17 00:00:00 2001
From: kremlin <kremlin@uglyman.kremlin.cc>
Date: Wed, 11 Feb 2015 13:57:16 -0600
Subject: [PATCH 1/1] add lab2 compass impl

---
 lab2_compass.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 lab2_compass.c

diff --git a/lab2_compass.c b/lab2_compass.c
new file mode 100644
index 0000000..e38095a
--- /dev/null
+++ b/lab2_compass.c
@@ -0,0 +1,129 @@
+#include <hidef.h>
+
+#include "derivative.h"
+#include "MC9S12XS128.h"
+
+/* laziness */
+#define null16 0x0000
+#define null8 0x00
+
+/* x, y, z enum */
+typedef enum { X, Y, Z } axis;
+
+/* gets magnetic field gauss val from lsm
+ * over spi & parses into passed int ptr
+ */
+void read_axis(axis x, int *hi, int *lo) {
+
+  switch(x) {
+
+    case X:
+
+      SPI0DR = 0x8900;
+      while(!SPI0SR_SPTEF);
+      *hi = SPI0DRL;
+
+      SPI0DR = 0x8800;
+      while(!SPI0SR_SPTEF);
+      *lo = SPI0DRL;
+
+      break;
+
+    case Y:
+
+      SPI0DR = 0x8B00;
+      while(!SPI0SR_SPTEF);
+      *hi = SPI0DRL;
+
+      SPI0DR = 0x8A00;
+      while(!SPI0SR_SPTEF);
+      *lo = SPI0DRL;
+
+      break;
+
+    case Z:
+
+      SPI0DR = 0x8D00;
+      while(!SPI0SR_SPTEF);
+      *hi = SPI0DRL;
+
+      SPI0DR = 0x8C00;
+      while(!SPI0SR_SPTEF);
+      *lo = SPI0DRL;
+
+      break;
+  }
+}
+
+/* parses 8 bit HI/LO pairs into x/y/z words */
+void parse_raw(int in[], long set[]) {
+
+  set[0] = (in[0] << 8) + in[1];
+  set[1] = (in[2] << 8) + in[3];
+  set[2] = (in[4] << 8) + in[5];
+}
+
+void configure_lsm() {
+
+  /* wait for SPI ready */
+  while(!SPI0SR_SPTEF);
+
+  /* fill transfer reg */
+  SPI0DR = 0x2474;
+
+  /* wait for transfer */
+  while(!SPI0SR_SPTEF);
+}
+
+void configure_spi() {
+
+  /* reroute spi I/O */
+  MODRR_MODRR4 = 1;
+
+  /* configure SPI */
+  SPI0CR1_SSOE = 1; /* enable slave select */
+  SPI0CR1_MSTR = 1; /* enable master */
+  SPI0CR1_CPOL = 0; /* clock polarity */
+  SPI0CR1_SPE = 1; /* enable system */
+  SPI0CR1_LSBFE = 1; /* set endian-ness */
+
+  SPI0CR2_XFRW = 1; /* set 16 bit width */
+  SPI0CR2_MODFEN = 1; /* enable slave select */
+}
+
+void main(void) {
+
+    /* SDA :: SPI in :: PM2 :: white
+     * SDO :: SPI out :: PM4 :: blue
+     * SCL :: clock :: PM5 :: yellow
+     * CS :: select :: PM3 :: green
+     */
+
+    /* positional vars & init */
+    long coords[3] = { null16, null16, null16 };
+    int coord8[6] = { null8, null8, null8, null8, null8, null8 };
+
+  /* configure SPI */
+  configure_spi();
+
+  /* configure LSM */
+  configure_lsm();
+
+  /* latch intrs.  */
+  EnableInterrupts;
+
+  for(;;) {
+
+    /* read x hi/lo */
+    read_axis(X, &coord8[0], &coord8[1]);
+
+    /* read y hi/lo */
+    read_axis(Y, &coord8[2], &coord8[3]);
+
+    /* read z hi/lo */
+    read_axis(Z, &coord8[4], &coord8[5]);;
+
+    /* parse raw bytes into x/y/z vars */
+    parse_raw(coord8, coords);
+  }
+}
-- 
2.41.0