mirror of
https://github.com/rtlsdrblog/rtl-sdr-blog.git
synced 2024-11-10 04:37:37 +01:00
rtl_adsb: 16 bit magnitudes
Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen
Steve Markgraf
parent
b656896f66
commit
c6a731a0dc
@ -54,16 +54,19 @@
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#define DEFAULT_BUF_LENGTH (16 * 16384)
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#define AUTO_GAIN -100
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#define MESSAGEGO 253
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#define OVERWRITE 254
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#define BADSAMPLE 255
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static pthread_t demod_thread;
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static sem_t data_ready;
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static volatile int do_exit = 0;
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static rtlsdr_dev_t *dev = NULL;
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/* look up table, could be made smaller */
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uint8_t pyth[129][129];
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uint16_t squares[256];
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/* todo, bundle these up in a struct */
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uint8_t *buffer;
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uint8_t *buffer; /* also abused for uint16_t */
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int verbose_output = 0;
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int short_output = 0;
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double quality = 1.0;
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@ -141,17 +144,7 @@ void display(int *frame, int len)
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fprintf(file, "--------------\n");
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}
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void pyth_precompute(void)
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{
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int x, y;
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double scale = 1.408 ; /* use the full 8 bits */
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for (x=0; x<129; x++) {
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for (y=0; y<129; y++) {
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pyth[x][y] = (uint8_t)round(scale * sqrt(x*x + y*y));
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}}
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}
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inline uint8_t abs8(uint8_t x)
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int abs8(int x)
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/* do not subtract 128 from the raw iq, this handles it */
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{
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if (x >= 128) {
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@ -159,18 +152,31 @@ inline uint8_t abs8(uint8_t x)
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return 128 - x;
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}
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void squares_precompute(void)
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/* equiv to abs(x-128) ^ 2 */
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{
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int i, j;
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// todo, check if this LUT is actually any faster
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for (i=0; i<256; i++) {
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j = abs8(i);
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squares[i] = (uint16_t)(j*j);
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}
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}
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int magnitute(uint8_t *buf, int len)
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/* takes i/q, changes buf in place, returns new len */
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/* takes i/q, changes buf in place (16 bit), returns new len (16 bit) */
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{
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int i;
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uint16_t *m;
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for (i=0; i<len; i+=2) {
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buf[i/2] = pyth[abs8(buf[i])][abs8(buf[i+1])];
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m = (uint16_t*)(&buf[i]);
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*m = squares[buf[i]] + squares[buf[i+1]];
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}
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return len/2;
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}
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inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
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/* takes 4 consecutive real samples, return 0 or 1, 255 on error */
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inline uint16_t single_manchester(uint16_t a, uint16_t b, uint16_t c, uint16_t d)
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/* takes 4 consecutive real samples, return 0 or 1, BADSAMPLE on error */
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{
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int bit, bit_p;
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bit_p = a > b;
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@ -181,9 +187,9 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
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if (quality == 0.5) {
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if ( bit && bit_p && b > c) {
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return 255;}
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return BADSAMPLE;}
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if (!bit && !bit_p && b < c) {
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return 255;}
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return BADSAMPLE;}
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return bit;
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}
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@ -196,7 +202,7 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
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return 0;}
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if (!bit && !bit_p && c < b) {
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return 0;}
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return 255;
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return BADSAMPLE;
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}
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if ( bit && bit_p && c > b && d < a) {
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@ -207,36 +213,36 @@ inline uint8_t single_manchester(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
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return 0;}
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if (!bit && !bit_p && c < b && d > a) {
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return 0;}
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return 255;
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return BADSAMPLE;
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}
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inline uint8_t min8(uint8_t a, uint8_t b)
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inline uint16_t min16(uint16_t a, uint16_t b)
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{
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return a<b ? a : b;
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}
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inline uint8_t max8(uint8_t a, uint8_t b)
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inline uint16_t max16(uint16_t a, uint16_t b)
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{
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return a>b ? a : b;
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}
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inline int preamble(uint8_t *buf, int len, int i)
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inline int preamble(uint16_t *buf, int i)
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/* returns 0/1 for preamble at index i */
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{
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int i2;
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uint8_t low = 0;
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uint8_t high = 255;
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uint16_t low = 0;
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uint16_t high = 65535;
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for (i2=0; i2<preamble_len; i2++) {
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switch (i2) {
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case 0:
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case 2:
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case 7:
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case 9:
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//high = min8(high, buf[i+i2]);
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//high = min16(high, buf[i+i2]);
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high = buf[i+i2];
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break;
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default:
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//low = max8(low, buf[i+i2]);
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//low = max16(low, buf[i+i2]);
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low = buf[i+i2];
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break;
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}
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@ -246,24 +252,24 @@ inline int preamble(uint8_t *buf, int len, int i)
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return 1;
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}
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void manchester(uint8_t *buf, int len)
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/* overwrites magnitude buffer with valid bits (255 on errors) */
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void manchester(uint16_t *buf, int len)
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/* overwrites magnitude buffer with valid bits (BADSAMPLE on errors) */
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{
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/* a and b hold old values to verify local manchester */
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uint8_t a=0, b=0;
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uint8_t bit;
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uint16_t a=0, b=0;
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uint16_t bit;
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int i, i2, start, errors;
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// todo, allow wrap across buffers
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i = 0;
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while (i < len) {
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/* find preamble */
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for ( ; i < (len - preamble_len); i++) {
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if (!preamble(buf, len, i)) {
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if (!preamble(buf, i)) {
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continue;}
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a = buf[i];
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b = buf[i+1];
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for (i2=0; i2<preamble_len; i2++) {
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buf[i+i2] = 253;}
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buf[i+i2] = MESSAGEGO;}
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i += preamble_len;
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break;
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}
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@ -274,25 +280,25 @@ void manchester(uint8_t *buf, int len)
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bit = single_manchester(a, b, buf[i], buf[i+1]);
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a = buf[i];
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b = buf[i+1];
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if (bit == 255) {
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if (bit == BADSAMPLE) {
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errors += 1;
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if (errors > allowed_errors) {
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buf[i2] = 255;
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buf[i2] = BADSAMPLE;
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break;
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} else {
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bit = a > b;
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/* these don't have to match the bit */
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a = 0;
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b = 255;
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b = 65535;
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}
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}
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buf[i] = buf[i+1] = 254; /* to be overwritten */
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buf[i] = buf[i+1] = OVERWRITE;
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buf[i2] = bit;
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}
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}
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}
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void messages(uint8_t *buf, int len)
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void messages(uint16_t *buf, int len)
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{
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int i, i2, start, preamble_found;
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int data_i, index, shift, frame_len;
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@ -343,8 +349,8 @@ static void *demod_thread_fn(void *arg)
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while (!do_exit) {
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sem_wait(&data_ready);
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len = magnitute(buffer, DEFAULT_BUF_LENGTH);
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manchester(buffer, len);
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messages(buffer, len);
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manchester((uint16_t*)buffer, len);
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messages((uint16_t*)buffer, len);
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}
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rtlsdr_cancel_async(dev);
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return 0;
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@ -363,7 +369,7 @@ int main(int argc, char **argv)
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int ppm_error = 0;
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char vendor[256], product[256], serial[256];
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sem_init(&data_ready, 0, 0);
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pyth_precompute();
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squares_precompute();
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while ((opt = getopt(argc, argv, "d:g:p:e:Q:VS")) != -1)
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{
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