1 files changed, 109 insertions, 0 deletions
diff --git a/stm32/app/gen/c.c b/stm32/app/gen/c.c
new file mode 100644
index 0000000..56e7237
--- /dev/null
+++ b/stm32/app/gen/c.c
@@ -0,0 +1,109 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+uint8_t crc_table[256];
+
+uint8_t flip_byte (uint8_t value)
+{
+  value = ((value >> 1) & 0x55) | ((value & 0x55) << 1);
+  value = ((value >> 2) & 0x33) | ((value & 0x33) << 2);
+  value = ((value >> 4) & 0x0F) | ((value & 0x0F) << 4);
+  return value;
+}
+
+
+uint8_t
+crc8 (uint8_t * data, size_t len)
+{
+  unsigned i, j;
+  uint8_t crc = 0, b;
+
+  for (i = 0; i < len; ++i, ++data)
+    {
+
+      b = *data;
+      for (j = 0; j < 8; j++)
+        {
+          if ((crc >> 7) ^ (b & 1))
+            {
+              crc = (crc << 1) ^ 7;
+            }
+          else
+            {
+              crc = crc << 1;
+            }
+
+          b >>= 1;
+        }
+    }
+  return crc;
+}
+
+void
+make_table (void)
+{
+  unsigned i;
+  unsigned j;
+  uint8_t  b;
+
+  for (i = 0; i < 256; ++i)
+    {
+      b = i;
+      for (j = 0; j < 8; j++)
+        {
+	  
+          if (b & 1)
+            {
+              b = (b >> 1 ) ^ 0xe0;
+            }
+          else
+            {
+              b = b >> 1;
+            }
+
+        }
+      crc_table[i] = b;
+    }
+}
+
+uint8_t
+crc8_better (uint8_t * data, size_t len)
+{
+  uint8_t crc = 0;
+  unsigned i;
+
+  for (i = 0; i < len; i++, data++)
+    {
+      crc = crc_table[crc ^ *data];
+    }
+
+  return flip_byte(crc);
+}
+
+
+
+int
+main (int argc, char *argv[])
+{
+  uint8_t fish[4] = "\5\0\1\301"; 
+  size_t l;
+
+  make_table ();
+
+  for (l=0;l<256;++l) {
+	printf("0x%02x, ",crc_table[l]);
+  }
+
+  printf("\n");
+
+  for (l=0;l<4;++l ) {
+  printf ("%u %02x %02x %02x\n",(unsigned)l, crc8 (fish, l), crc8_better (fish, l), fish[l]);
+  }
+
+  
+
+  return 0;
+}
+
+