mordae/pico-sdr
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Dither LO phase to reduce artifacts

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This commit is contained in:
Jan Hamal Dvořák 2024-07-09 20:32:58 +02:00
parent ff6001b0da
commit 7af68838e7
1 changed files with 41 additions and 5 deletions
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46
src/main.c
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@ -83,6 +83,14 @@ static queue_t iq_queue;
static uint8_t iq_queue_buffer[IQ_QUEUE_LEN][IQ_BLOCK_LEN];
static size_t iq_queue_pos = 0;
static uint32_t rnd = 0;
inline static uint32_t rnd_next()
{
rnd = rnd * 0x41c64e6d + 12345;
return rnd;
}
static void bias_set_delay(int delay)
{
delay += 200;
@ -236,25 +244,50 @@ static void adder_init()
pio_sm_set_enabled(pio1, 3, true);
}
#define STEP_BASE ((UINT_MAX + 1.0) / CLK_SYS_HZ)
static uint32_t freq_step = 1;
static void lo_generate(uint32_t *buf, double freq, uint32_t phase)
{
static const double base = (UINT_MAX + 1.0) / CLK_SYS_HZ;
freq_step = STEP_BASE * freq;
uint32_t step = base * freq;
unsigned down = 3 + __builtin_clz(freq_step);
for (size_t i = 0; i < LO_WORDS; i++) {
unsigned bits = 0;
uint32_t bits = 0;
int shift = (rnd_next() >> down) - (rnd_next() >> down) + (rnd_next() >> down) -
(rnd_next() >> down);
for (int j = 0; j < 32; j++) {
bits |= phase >> 31;
bits |= (phase + shift) >> 31;
bits <<= 1;
phase += step;
phase += freq_step;
}
buf[i] = bits;
}
}
static void lo_tweak(uint32_t *buf, uint32_t phase)
{
static size_t i = 0;
uint32_t bits = 0;
unsigned down = 3 + __builtin_clz(freq_step);
phase += freq_step * i * 32;
for (int j = 0; j < 32; j++) {
int shift = (rnd_next() >> down) - (rnd_next() >> down) + (rnd_next() >> down) -
(rnd_next() >> down);
bits |= (phase + shift) >> 31;
bits <<= 1;
phase += freq_step;
}
buf[i] = bits;
i = (i + 1) & (LO_WORDS - 1);
}
static void rx_lo_init(double req_freq, bool align)
{
const double step_hz = (double)CLK_SYS_HZ / (4 << LO_BITS_DEPTH);
@ -568,6 +601,9 @@ static void rf_rx(void)
if (queue_try_add(&iq_queue, &block)) {
iq_queue_pos = (iq_queue_pos + 1) & (IQ_QUEUE_LEN - 1);
}
lo_tweak(lo_cos, COS_PHASE);
lo_tweak(lo_sin, SIN_PHASE);
}
}