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authorKyle Keen <keenerd@gmail.com>2013-01-29 20:31:49 -0500
committerSteve Markgraf <steve@steve-m.de>2013-01-30 20:24:24 +0100
commitc6a731a0dcff882edb4777a816865f525966464d (patch)
tree05ff4af48a6f5e95442ed86f09372d59607ab8b8 /src/rtl_adsb.c
parentb656896f668c7887bbf2cefb2047fe9078de5ae2 (diff)
rtl_adsb: 16 bit magnitudes
Signed-off-by: Steve Markgraf <steve@steve-m.de>
Diffstat (limited to 'src/rtl_adsb.c')
-rw-r--r--src/rtl_adsb.c92
1 files changed, 49 insertions, 43 deletions
diff --git a/src/rtl_adsb.c b/src/rtl_adsb.c
index 2fb7418..a625d31 100644
--- a/src/rtl_adsb.c
+++ b/src/rtl_adsb.c
@@ -54,16 +54,19 @@
#define DEFAULT_BUF_LENGTH (16 * 16384)
#define AUTO_GAIN -100
+#define MESSAGEGO 253
+#define OVERWRITE 254
+#define BADSAMPLE 255
+
static pthread_t demod_thread;
static sem_t data_ready;
static volatile int do_exit = 0;
static rtlsdr_dev_t *dev = NULL;
-/* look up table, could be made smaller */
-uint8_t pyth[129][129];
+uint16_t squares[256];
/* todo, bundle these up in a struct */
-uint8_t *buffer;
+uint8_t *buffer; /* also abused for uint16_t */
int verbose_output = 0;
int short_output = 0;
double quality = 1.0;
@@ -141,17 +144,7 @@ void display(int *frame, int len)
fprintf(file, "--------------\n");
}
-void pyth_precompute(void)
-{
- int x, y;
- double scale = 1.408 ; /* use the full 8 bits */
- for (x=0; x<129; x++) {
- for (y=0; y<129; y++) {
- pyth[x][y] = (uint8_t)round(scale * sqrt(x*x + y*y));
- }}
-}
-
-inline uint8_t abs8(uint8_t x)
+int abs8(int x)
/* do not subtract 128 from the raw iq, this handles it */
{
if (x >= 128) {
@@ -159,18 +152,31 @@ inline uint8_t abs8(uint8_t x)
return 128 - x;
}
+void squares_precompute(void)
+/* equiv to abs(x-128) ^ 2 */
+{
+ int i, j;
+ // todo, check if this LUT is actually any faster
+ for (i=0; i<256; i++) {
+ j = abs8(i);
+ squares[i] = (uint16_t)(j*j);
+ }
+}
+
int magnitute(uint8_t *buf, int len)
-/* takes i/q, changes buf in place, returns new len */
+/* takes i/q, changes buf in place (16 bit), returns new len (16 bit) */
{
int i;
+ uint16_t *m;
for (i=0; i<len; i+=2) {
- buf[i/2] = pyth[abs8(buf[i])][abs8(buf[i+1])];
+ m = (uint16_t*)(&buf[i]);
+ *m = squares[buf[i]] + squares[buf[i+1]];
}
return len/2;
}
-inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
-/* takes 4 consecutive real samples, return 0 or 1, 255 on error */
+inline uint16_t single_manchester(uint16_t a, uint16_t b, uint16_t c, uint16_t d)
+/* takes 4 consecutive real samples, return 0 or 1, BADSAMPLE on error */
{
int bit, bit_p;
bit_p = a > b;
@@ -181,9 +187,9 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
if (quality == 0.5) {
if ( bit && bit_p && b > c) {
- return 255;}
+ return BADSAMPLE;}
if (!bit && !bit_p && b < c) {
- return 255;}
+ return BADSAMPLE;}
return bit;
}
@@ -196,7 +202,7 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
return 0;}
if (!bit && !bit_p && c < b) {
return 0;}
- return 255;
+ return BADSAMPLE;
}
if ( bit && bit_p && c > b && d < a) {
@@ -207,36 +213,36 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
return 0;}
if (!bit && !bit_p && c < b && d > a) {
return 0;}
- return 255;
+ return BADSAMPLE;
}
-inline uint8_t min8(uint8_t a, uint8_t b)
+inline uint16_t min16(uint16_t a, uint16_t b)
{
return a<b ? a : b;
}
-inline uint8_t max8(uint8_t a, uint8_t b)
+inline uint16_t max16(uint16_t a, uint16_t b)
{
return a>b ? a : b;
}
-inline int preamble(uint8_t *buf, int len, int i)
+inline int preamble(uint16_t *buf, int i)
/* returns 0/1 for preamble at index i */
{
int i2;
- uint8_t low = 0;
- uint8_t high = 255;
+ uint16_t low = 0;
+ uint16_t high = 65535;
for (i2=0; i2<preamble_len; i2++) {
switch (i2) {
case 0:
case 2:
case 7:
case 9:
- //high = min8(high, buf[i+i2]);
+ //high = min16(high, buf[i+i2]);
high = buf[i+i2];
break;
default:
- //low = max8(low, buf[i+i2]);
+ //low = max16(low, buf[i+i2]);
low = buf[i+i2];
break;
}
@@ -246,24 +252,24 @@ inline int preamble(uint8_t *buf, int len, int i)
return 1;
}
-void manchester(uint8_t *buf, int len)
-/* overwrites magnitude buffer with valid bits (255 on errors) */
+void manchester(uint16_t *buf, int len)
+/* overwrites magnitude buffer with valid bits (BADSAMPLE on errors) */
{
/* a and b hold old values to verify local manchester */
- uint8_t a=0, b=0;
- uint8_t bit;
+ uint16_t a=0, b=0;
+ uint16_t bit;
int i, i2, start, errors;
// todo, allow wrap across buffers
i = 0;
while (i < len) {
/* find preamble */
for ( ; i < (len - preamble_len); i++) {
- if (!preamble(buf, len, i)) {
+ if (!preamble(buf, i)) {
continue;}
a = buf[i];
b = buf[i+1];
for (i2=0; i2<preamble_len; i2++) {
- buf[i+i2] = 253;}
+ buf[i+i2] = MESSAGEGO;}
i += preamble_len;
break;
}
@@ -274,25 +280,25 @@ void manchester(uint8_t *buf, int len)
bit = single_manchester(a, b, buf[i], buf[i+1]);
a = buf[i];
b = buf[i+1];
- if (bit == 255) {
+ if (bit == BADSAMPLE) {
errors += 1;
if (errors > allowed_errors) {
- buf[i2] = 255;
+ buf[i2] = BADSAMPLE;
break;
} else {
bit = a > b;
/* these don't have to match the bit */
a = 0;
- b = 255;
+ b = 65535;
}
}
- buf[i] = buf[i+1] = 254; /* to be overwritten */
+ buf[i] = buf[i+1] = OVERWRITE;
buf[i2] = bit;
}
}
}
-void messages(uint8_t *buf, int len)
+void messages(uint16_t *buf, int len)
{
int i, i2, start, preamble_found;
int data_i, index, shift, frame_len;
@@ -343,8 +349,8 @@ static void *demod_thread_fn(void *arg)
while (!do_exit) {
sem_wait(&data_ready);
len = magnitute(buffer, DEFAULT_BUF_LENGTH);
- manchester(buffer, len);
- messages(buffer, len);
+ manchester((uint16_t*)buffer, len);
+ messages((uint16_t*)buffer, len);
}
rtlsdr_cancel_async(dev);
return 0;
@@ -363,7 +369,7 @@ int main(int argc, char **argv)
int ppm_error = 0;
char vendor[256], product[256], serial[256];
sem_init(&data_ready, 0, 0);
- pyth_precompute();
+ squares_precompute();
while ((opt = getopt(argc, argv, "d:g:p:e:Q:VS")) != -1)
{