mordae/pico-sdr
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Improve LO synthesis precision to 17.9 Hz

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This commit is contained in:
Jan Hamal Dvořák 2024-07-26 21:37:35 +02:00
parent f7d2dd3629
commit 24d6acdb53
1 changed files with 33 additions and 20 deletions
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53
src/main.c
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@ -39,9 +39,17 @@
#define IQ_BLOCK_LEN (2 * IQ_SAMPLES)
#define IQ_QUEUE_LEN 8
#define LO_BITS_DEPTH 15
#define LO_WORDS (1 << (LO_BITS_DEPTH - 2))
static uint32_t lo_cos[LO_WORDS] __attribute__((__aligned__(1 << LO_BITS_DEPTH)));
#define LO_NUM_PHASES 64
#define LO_PHASE_BITS 10
#define LO_PHASE_WORDS (1 << (LO_PHASE_BITS - 2))
#define LO_COS_PHASES 4096
#define LO_EFFECTIVE_BITS (32 * LO_PHASE_WORDS * LO_COS_PHASES)
static uint32_t lo_phase[LO_NUM_PHASES][LO_PHASE_WORDS]
__attribute__((__aligned__(LO_NUM_PHASES * 4 * LO_PHASE_WORDS)));
static const uint32_t *lo_cos_phases[LO_COS_PHASES]
__attribute__((__aligned__(1 << LO_PHASE_BITS)));
#define DECIMATE 4
#define RX_STRIDE (2 * IQ_SAMPLES * DECIMATE)
@ -63,9 +71,6 @@ static int gains[NUM_GAINS] = { 0, 9, 14, 27, 37, 77, 87, 125, 144, 157
static int sample_rate = INIT_SAMPLE_RATE;
static int gain = INIT_GAIN;
#define SIN_PHASE (0u)
#define COS_PHASE (3u << 30)
static int dma_ch_rx1 = -1;
static int dma_ch_rx2 = -1;
@ -245,19 +250,16 @@ static void init_ad()
}
#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 void lo_generate_phase(uint32_t *buf, size_t len, uint32_t step, uint32_t phase)
{
freq_step = STEP_BASE * freq;
for (size_t i = 0; i < LO_WORDS; i++) {
for (size_t i = 0; i < len; i++) {
uint32_t bits = 0;
for (int j = 0; j < 32; j++) {
bits |= phase >> 31;
bits <<= 1;
phase += freq_step;
phase += step;
}
buf[i] = bits;
@ -266,13 +268,25 @@ static void lo_generate(uint32_t *buf, double freq, uint32_t phase)
static void rx_lo_init(double req_freq, bool align)
{
const double step_hz = (double)CLK_SYS_HZ / (8 << LO_BITS_DEPTH);
const double step_hz = (double)CLK_SYS_HZ / (LO_EFFECTIVE_BITS / 2.0);
double freq = req_freq;
if (align)
freq = round(freq / step_hz) * step_hz;
lo_generate(lo_cos, freq, COS_PHASE);
uint32_t step = STEP_BASE * freq;
for (uint32_t i = 0; i < LO_NUM_PHASES; i++)
lo_generate_phase(lo_phase[i], LO_PHASE_WORDS, step,
i << (__builtin_clz(LO_NUM_PHASES) + 1));
uint32_t phase_step = step * 32 * LO_PHASE_WORDS;
uint32_t phase = 0;
for (uint32_t i = 0; i < LO_COS_PHASES; i++) {
lo_cos_phases[i] = lo_phase[phase >> (__builtin_clz(LO_NUM_PHASES) + 1)];
phase += phase_step;
}
}
static const uint32_t samp_insn = 5;
@ -315,19 +329,18 @@ static void rf_rx_start()
channel_config_set_transfer_data_size(&dma_conf, DMA_SIZE_32);
channel_config_set_read_increment(&dma_conf, true);
channel_config_set_write_increment(&dma_conf, false);
channel_config_set_ring(&dma_conf, GPIO_IN, LO_BITS_DEPTH);
channel_config_set_dreq(&dma_conf, pio_get_dreq(PIO, LO_SM, GPIO_OUT));
channel_config_set_chain_to(&dma_conf, dma_ch_mix2);
dma_channel_configure(dma_ch_mix1, &dma_conf, &PIO->txf[LO_SM], lo_cos, UINT_MAX, false);
channel_config_set_ring(&dma_conf, GPIO_IN, LO_PHASE_BITS);
dma_channel_configure(dma_ch_mix1, &dma_conf, &dma_hw->ch[dma_ch_mix2].al3_read_addr_trig,
lo_cos_phases, 1, false);
dma_conf = dma_channel_get_default_config(dma_ch_mix2);
channel_config_set_transfer_data_size(&dma_conf, DMA_SIZE_32);
channel_config_set_read_increment(&dma_conf, true);
channel_config_set_write_increment(&dma_conf, false);
channel_config_set_ring(&dma_conf, GPIO_IN, LO_BITS_DEPTH);
channel_config_set_dreq(&dma_conf, pio_get_dreq(PIO, LO_SM, GPIO_OUT));
channel_config_set_chain_to(&dma_conf, dma_ch_mix1);
dma_channel_configure(dma_ch_mix2, &dma_conf, &PIO->txf[LO_SM], lo_cos, UINT_MAX, false);
dma_channel_configure(dma_ch_mix2, &dma_conf, &PIO->txf[LO_SM], NULL, LO_PHASE_WORDS,
false);
/* Pacing timer for the sampling script trigger channel. */
dma_timer_set_fraction(dma_t_samp, 1, CLK_SYS_HZ / (sample_rate * DECIMATE));