Repo re-org

1 files changed, 44 insertions, 0 deletions

diff --git a/reset-controller/fw/src/protocol.c b/reset-controller/fw/src/protocol.c
new file mode 100644
index 0000000..6b7d8b7
--- /dev/null
+++ b/reset-controller/fw/src/protocol.c
@@ -0,0 +1,44 @@
+
+#include <assert.h>
+
+#include "sr_global.h"
+#include "dsss_demod.h"
+#include "con_usart.h"
+#include "rslib.h"
+#include "crypto.h"
+
+void handle_dsss_received(uint8_t data[static TRANSMISSION_SYMBOLS]) {
+    /* Console status output */
+    con_printf("DSSS data received: ");
+    for (int i=0; i<TRANSMISSION_SYMBOLS; i++) {
+        int x = (data[i]>>1) * (data[i]&1 ? 1 : -1);
+        con_printf("%3d ", x);
+    }
+    con_printf("\r\n");
+
+    /* Run reed-solomon error correction */
+    const int sym_bits = DSSS_GOLD_CODE_NBITS + 1; /* +1 for amplitude sign bit */
+    /* TODO identify erasures in DSSS demod layer */
+    (void) rslib_decode(sym_bits, TRANSMISSION_SYMBOLS, (char *)data);
+    /* TODO error detection & handling */
+
+    /* Re-bit-pack data buffer to be bit-continuous:
+     *      [ . . a b  c d e f ] [ . . g h  i j k l ] [ . . m n  o p q r ] ...
+     *  ==> [ a b c d  e f g h ] [ i j k l  m n o p ] [ q r ...          ] ...
+     */
+    static_assert((TRANSMISSION_SYMBOLS - NPAR) * (DSSS_GOLD_CODE_NBITS + 1) == OOB_TRIGGER_LEN * 8);
+    for (uint8_t i=0, j=0; i < TRANSMISSION_SYMBOLS - NPAR; i++, j += sym_bits) {
+        uint32_t sym = data[i]; /* [ ... | . . X X  X X X X ] for 5-bit dsss */
+        data[i] = 0; /* clear for output */
+
+        sym <<= 8-sym_bits; /* left-align: [ ... | X X X X  X X . . ] */
+        sym <<= 8; /* shift to second byte: [ ... | X X X X  X X . . | . . . .  . . . . ]*/
+        sym >>= (j%8); /* shift to bit write offset: [ ... | . . . .  X X X X | X X . .  . . . . ] for offset 4 */
+        data[j/8] |= sym >> 8; /* write upper byte */
+        data[j/8 + 1] |= sym & 0xff; /* write lower byte */
+    }
+
+    /* hand off to crypto.c */ 
+    oob_message_received(data);
+}
+