static int16_t iir_x[2];
static int16_t iir_y[2];
+
static uint8_t sampled_bits;
static uint8_t found_bits;
static uint8_t demod_bits;
#define BIT_DIFFER(bitline1, bitline2) (((bitline1) ^ (bitline2)) & 0x01)
#define EDGE_FOUND(bitline) BIT_DIFFER((bitline), (bitline) >> 1)
+static uint16_t preamble_len;
+static uint16_t trailer_len;
+
static void hdlc_parse(bool bit)
{
demod_bits <<= 1;
/* HDLC Flag */
if (demod_bits == HDLC_FLAG)
{
- if (!fifo_isfull_locked(&rx_fifo))
+ if (!fifo_isfull(&rx_fifo))
{
fifo_push(&rx_fifo, HDLC_FLAG);
hdlc_rxstart = true;
}
else
hdlc_rxstart = false;
+
hdlc_currchar = 0;
hdlc_bit_idx = 0;
return;
{
if ((hdlc_currchar == HDLC_FLAG
|| hdlc_currchar == HDLC_RESET
- || hdlc_currchar == AX25_ESC)
- && !fifo_isfull_locked(&rx_fifo))
- fifo_push(&rx_fifo, AX25_ESC);
- else
- hdlc_rxstart = false;
+ || hdlc_currchar == AX25_ESC))
+ {
+ if (!fifo_isfull(&rx_fifo))
+ fifo_push(&rx_fifo, AX25_ESC);
+ else
+ hdlc_rxstart = false;
+ }
- if (!fifo_isfull_locked(&rx_fifo))
+ if (!fifo_isfull(&rx_fifo))
fifo_push(&rx_fifo, hdlc_currchar);
else
hdlc_rxstart = false;
/*
* Frequency discrimination is achieved by simply multiplying
- * the sample with a delayed sample of (bits per sample) / 2.
- * Then the signal is lowpass filtered with a first order, 600 Hz
- * Butterworth filter.
+ * the sample with a delayed sample of (samples per bit) / 2.
+ * Then the signal is lowpass filtered with a first order,
+ * 600 Hz filter. The filter implementation is selectable
+ * through the CONFIG_AFSK_FILTER config variable.
*/
iir_x[0] = iir_x[1];
- iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) >> 2;
+
+ #if (CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH)
+ iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) >> 2;
+ //iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) / 6.027339492;
+ #elif (CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV)
+ iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) >> 2;
+ //iir_x[1] = ((int8_t)fifo_pop(&delay_fifo) * curr_sample) / 3.558147322;
+ #else
+ #error Filter type not found!
+ #endif
+
iir_y[0] = iir_y[1];
- /*
- * This strange sum + shift is an optimization for iir_y[0] * 0.668.
- * iir * 0.668 ~= (iir * 21) / 32 =
- * = (iir * 16) / 32 + (iir * 4) / 32 + iir / 32 =
- * = iir / 2 + iir / 8 + iir / 32 =
- * = iir >> 1 + iir >> 3 + iir >> 5
- */
- iir_y[1] = iir_x[0] + iir_x[1] + (iir_y[0] >> 1) + (iir_y[0] >> 3) + (iir_y[0] >> 5);
+ #if CONFIG_AFSK_FILTER == AFSK_BUTTERWORTH
+ /*
+ * This strange sum + shift is an optimization for iir_y[0] * 0.668.
+ * iir * 0.668 ~= (iir * 21) / 32 =
+ * = (iir * 16) / 32 + (iir * 4) / 32 + iir / 32 =
+ * = iir / 2 + iir / 8 + iir / 32 =
+ * = iir >> 1 + iir >> 3 + iir >> 5
+ */
+ iir_y[1] = iir_x[0] + iir_x[1] + (iir_y[0] >> 1) + (iir_y[0] >> 3) + (iir_y[0] >> 5);
+ //iir_y[1] = iir_x[0] + iir_x[1] + iir_y[0] * 0.6681786379;
+ #elif CONFIG_AFSK_FILTER == AFSK_CHEBYSHEV
+ /*
+ * This should be (iir_y[0] * 0.438) but
+ * (iir_y[0] >> 1) is a faster approximation :-)
+ */
+ iir_y[1] = iir_x[0] + iir_x[1] + (iir_y[0] >> 1);
+ //iir_y[1] = iir_x[0] + iir_x[1] + iir_y[0] * 0.4379097269;
+ #endif
/* Save this sampled bit in a delay line */
sampled_bits <<= 1;
found_bits <<= 1;
/*
- * TODO: maybe a better algorithm to find the sample bit
- * other than reading the last one.
+ * Determine bit value by reading the last 3 sampled bits.
+ * If the number of ones is two or greater, the bit value is a 1,
+ * otherwise is a 0.
*/
- found_bits |= sampled_bits & 1;
+ uint8_t bits = sampled_bits & 0x07;
+ if (bits == 0x07 // 111, 3 bits set to 1
+ || bits == 0x06 // 110, 2 bits
+ || bits == 0x05 // 101, 2 bits
+ || bits == 0x03 // 011, 2 bits
+ )
+ found_bits |= 1;
/*
* NRZI coding: if 2 consecutive bits have the same value
phase_acc = 0;
stuff_cnt = 0;
sending = true;
+ preamble_len = DIV_ROUND(CONFIG_AFSK_PREAMBLE_LEN * BITRATE, 8000);
AFSK_DAC_IRQ_START();
}
+ ATOMIC(trailer_len = DIV_ROUND(CONFIG_AFSK_TRAILER_LEN * BITRATE, 8000));
}
#define BIT_STUFF_LEN 5
if (tx_bit == 0)
{
/* We have just finished transimitting a char, get a new one. */
- if (fifo_isempty(&tx_fifo))
+ if (fifo_isempty(&tx_fifo) && trailer_len == 0)
{
AFSK_DAC_IRQ_STOP();
sending = false;
stuff_cnt = 0;
bit_stuff = true;
- curr_out = fifo_pop(&tx_fifo);
+
+ /*
+ * Handle preamble and trailer
+ */
+ if (preamble_len == 0)
+ {
+ if (fifo_isempty(&tx_fifo))
+ {
+ trailer_len--;
+ curr_out = HDLC_FLAG;
+ }
+ else
+ curr_out = fifo_pop(&tx_fifo);
+ }
+ else
+ {
+ preamble_len--;
+ curr_out = HDLC_FLAG;
+ }
/* Handle char escape */
if (curr_out == AX25_ESC)
ticks_t start = timer_clock();
#endif
- do
+ while (fifo_isempty_locked(&rx_fifo));
{
cpu_relax();
#if CONFIG_AFSK_RXTIMEOUT != -1
return buf - (uint8_t *)_buf;
#endif
}
- while (fifo_isempty_locked(&rx_fifo));
*buf++ = fifo_pop_locked(&rx_fifo);
}
projects / bertos.git / blobdiff