driver_sirf.c 50BPS parity check seems to work. No wonder there are

so many parity bits, the data stream is a mess.

1 files changed, 36 insertions, 7 deletions

diff --git a/driver_sirf.c b/driver_sirf.c
index 2cf8b6b0..c8ca0020 100644
--- a/driver_sirf.c
+++ b/driver_sirf.c
@@ -432,6 +432,32 @@ static gps_mask_t sirf_msg_swversion(struct gps_device_t *session,
 }
 #endif /* ALLOW_RECONFIGURE */
 
+#ifdef __UNUSED__
+static unsigned int isgps_parity1( unsigned int value ) 
+{
+	unsigned int result;
+
+	/* D30 is XOR of D30* d3 d5 d6 d8 d9 d10 d11 d13 d15 d19 d22 d23 d24 */
+	result ^= ((value >> 31) & 1);	/* D29* to D30 */
+	result ^= ((value >> 27) & 1);	/*  d3 to D30	*/
+	result ^= ((value >> 25) & 1);	/*  d5 to D30	*/
+	result ^= ((value >> 24) & 1);	/*  d6 to D30	*/
+	result ^= ((value >> 22) & 1);	/*  d8 to D30	*/
+	result ^= ((value >> 21) & 1);	/*  d9 to D30	*/
+	result ^= ((value >> 20) & 1);	/* d10 to D30	*/
+	result ^= ((value >> 19) & 1);	/* d11 to D30	*/
+	result ^= ((value >> 17) & 1);	/* d13 to D30	*/
+	result ^= ((value >> 15) & 1);	/* d15 to D30	*/
+	result ^= ((value >> 11) & 1);	/* d19 to D30	*/
+	result ^= ((value >>  8) & 1);	/* d22 to D30	*/
+	result ^= ((value >>  7) & 1);	/* d23 to D30	*/
+	result ^= ((value >>  6) & 1);	/* d24 to D30	*/
+
+	return result;
+
+}
+#endif
+
 static gps_mask_t sirf_msg_navdata(struct gps_device_t *session,
 				   unsigned char *buf, size_t len)
 {
@@ -455,17 +481,20 @@ static gps_mask_t sirf_msg_navdata(struct gps_device_t *session,
      * 2 bits are the bottom two parity bits from the previous word. Mask and
      * shift these away to leave us with 3 data bytes per word */
 
+    /* gotta do the first word by hand, D29* and D30* seem missing */
     words[0] = ((unsigned int)getbeul(buf, 3) & 0x3fffffff) >> 6;
     preamble = words[0] >> 16;
     if (preamble == 0x8b) {
 	preamble ^= 0xff;
-	words[0] ^= 0xffffC0;
+	words[0] ^= 0x3fffC0;
     }
 
     parity1 = parity9 = 0;
     for (i = 1; i < 10; i++) {
 	int invert;
-	words[i] = (unsigned int)getbeul(buf, 4 * i + 3);
+	unsigned int word;
+	word = (unsigned int)getbeul(buf, 4 * i + 3);
+	words[i] = word;
 	switch (i) {
 	case 1:
 	    parity1 = words[1] & 0x3;
@@ -478,14 +507,14 @@ static gps_mask_t sirf_msg_navdata(struct gps_device_t *session,
 	invert = (words[i] & 0x40000000) ? 1 : 0;
 	/* inverted data, invert it back */
 	if (invert) {
-	    words[i] ^= 0xffffffC0;
+	    words[i] ^= 0x3fffffC0;
 	}
-	parity = isgps_parity( getbeul(buf, 4 * i + 3));
-	if ( parity != (getbeul(buf, 4  * i + 3) & 0x3f) ) {
+	parity = isgps_parity( words[i] ) ;
+	if ( parity != (words[i] & 0x3F) ) {
 	    gpsd_report(LOG_WARN, 
 	    	"SiRF: 50BPS parity fail words[%d] 0x%x != 0x%x\n", i,
-		    parity, ( getbeul(buf, 4 * i + 3) & 0x3f));
-	    //return 0;
+		    parity, ( words[i] & 0x1));
+	    return 0;
 	}
 	words[i] = (words[i] & 0x3fffffff) >> 6;
     }