Some documentation

[proxmark3-svn] / armsrc / lfops.c

diff --git a/armsrc/lfops.c b/armsrc/lfops.c
index f5040850c50cd2b1f93dfdf979bdbd74b463cfe2..3cd2bc36db70b5e22501654fc6beea0867408a53 100644 (file)
--- a/armsrc/lfops.c
+++ b/armsrc/lfops.c
@@ -16,6 +16,97 @@
 #include "string.h"
 #include "lfdemod.h"
 
+typedef struct {
+       uint8_t * buffer;
+       uint32_t numbits;
+       uint8_t position;
+} BitstreamOut;
+/**
+ * @brief Pushes bit onto the stream
+ * @param stream
+ * @param bit
+ */
+void pushBit( BitstreamOut* stream, bool bit)
+{
+       int bytepos = stream->position >> 3; // divide by 8
+       int bitpos = stream->position & 7;
+       *(stream->buffer+bytepos) |= (bit & 1) <<  (7 - bitpos);
+       stream->position++;
+       stream->numbits++;
+}
+/**
+ * @brief Does LF sample acquisition, this method implements decimation and quantization in order to
+ * be able to provide longer sample traces.
+ * @param decimation - how much should the signal be decimated. A decimation of 1 means every sample, 2 means
+ * every other sample, etc.
+ * @param bits_per_sample - bits per sample. Max 8, min 1 bit per sample.
+ * @param trigger_threshold - a threshold. The sampling won't commence until this threshold has been reached. Set
+ * to -1 to ignore threshold.
+ * @param averaging If set to true, decimation will use averaging, so that if e.g. decimation is 3, the sample
+ * value that will be used is the average value of the three samples.
+ * @return the number of bits occupied by the samples.
+ */
+uint8_t DoAcquisition(int decimation, int bits_per_sample, int trigger_threshold, bool averaging)
+{
+       //A decimation of 2 means we keep every 2nd sample
+       //A decimation of 3 means we keep 1 in 3 samples.
+       //A quantization of 1 means one bit is discarded from the sample (division by 2).
+       uint8_t *dest = (uint8_t *)BigBuf;
+       int bufsize = BIGBUF_SIZE;
+       memset(dest, 0, bufsize);
+       if(bits_per_sample < 1) bits_per_sample = 1;
+       if(bits_per_sample > 8) bits_per_sample = 8;
+
+       // Use a bit stream to handle the output
+       BitstreamOut data = { dest , 0, 0};
+       int sample_counter = 0;
+       uint8_t sample = 0;
+       //If we want to do averaging
+       uint32_t sample_sum =0 ;
+       uint32_t sample_total_numbers =0 ;
+       uint32_t sample_total_saved =0 ;
+
+       for(;;) {
+               WDT_HIT();
+               if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_TXRDY) {
+                       AT91C_BASE_SSC->SSC_THR = 0x43;
+                       LED_D_ON();
+               }
+               if (AT91C_BASE_SSC->SSC_SR & AT91C_SSC_RXRDY) {
+                       sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
+                       if (trigger_threshold != -1 && sample < trigger_threshold)
+                               continue;
+                       sample_total_numbers++;
+
+                       LED_D_OFF();
+                       trigger_threshold = -1;
+                       sample_counter++;
+                       sample_sum += sample;
+                       //Check decimation
+                       if(sample_counter < decimation) continue;
+                       //Averaging
+                       if(averaging) sample = sample_sum / decimation;
+
+                       sample_counter = 0;
+                       sample_sum =0;
+                       sample_total_saved ++;
+                       pushBit(&data, sample & 0x80);
+                       if(bits_per_sample > 1) pushBit(&data, sample & 0x40);
+                       if(bits_per_sample > 2) pushBit(&data, sample & 0x20);
+                       if(bits_per_sample > 3) pushBit(&data, sample & 0x10);
+                       if(bits_per_sample > 4) pushBit(&data, sample & 0x08);
+                       if(bits_per_sample > 5) pushBit(&data, sample & 0x04);
+                       if(bits_per_sample > 6) pushBit(&data, sample & 0x02);
+                       if(bits_per_sample > 7) pushBit(&data, sample & 0x01);
+
+                       if((data.numbits >> 3) +1  >= bufsize) break;
+               }
+       }
+       Dbprintf("Done, saved %l out of %l seen samples.",sample_total_saved, sample_total_numbers);
+
+       return data.numbits;
+}
+
 
 /**
 * Does the sample acquisition. If threshold is specified, the actual sampling