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picofreq.c
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picofreq.c
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// Accurate frequency measurement using a Pi Pico RP2040
// See https://iosoft.blog/picofreq for detailed description
//
// Copyright (c) Jeremy P Bentham 2023
// v0.01 JPB 28/7/23 Adapted from QSpeed v0.14
// v0.02 JPB 29/7/23 Removed redundant code
#define VERSION "0.02"
#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "hardware/clocks.h"
#include "hardware/pwm.h"
#include "hardware/dma.h"
// Set zero to use edge-counter, 1 to use edge-timer (reciprocal measurement)
#define USE_EDGE_TIMER 0
// GPIO pin numbers
#define FREQ_IN_PIN 7
#define GATE_TIMER_PIN 0
// Parameters for edge-counter gating
#define TIMER_PRESCALE 250 // 8-bit value
#define TIMER_WRAP 125000 // 17-bit value
#define SAMPLE_FREQ (125000000 / (TIMER_PRESCALE * TIMER_WRAP))
// Parameters for edge-timer: number of samples, and sample interval
#define NUM_EDGE_TIMES 11
#define EDGE_WAIT_USEC 200001
uint gate_dma_chan, gate_dma_dreq, csr_stopval;
uint counter_slice, gate_slice;
uint counter_lastval, counter_overflow;
uint timer_dma_chan;
uint edge_times[NUM_EDGE_TIMES];
void gate_timer_init(int pin);
void freq_counter_init(int pin);
void freq_counter_start(void);
bool freq_counter_value_ready(void);
int freq_counter_value(void);
int edge_counter_frequency(void);
void edge_timer_init(void);
void edge_timer_start(void);
int edge_timer_value(void);
float edge_timer_frequency(void);
bool ustimeout(uint *tickp, uint usec);
void msdelay(int msec);
int main()
{
const uint LED_PIN = PICO_DEFAULT_LED_PIN;
uint ledon=0;
stdio_init_all();
gpio_init(LED_PIN);
gpio_set_dir(LED_PIN, GPIO_OUT);
freq_counter_init(FREQ_IN_PIN);
#if USE_EDGE_TIMER
edge_timer_init();
#else
gate_timer_init(GATE_TIMER_PIN);
#endif
printf("PicoFreq v" VERSION "\n");
while (true)
{
gpio_put(LED_PIN, (ledon = !ledon));
#if USE_EDGE_TIMER
memset(edge_times, 0, sizeof(edge_times));
edge_timer_start();
uint edge_ticks;
ustimeout(&edge_ticks, 0);
while (!ustimeout(&edge_ticks, EDGE_WAIT_USEC))
{
}
printf("Frequency %5.3f Hz\n", edge_timer_frequency());
#else
freq_counter_start();
while (!freq_counter_value_ready())
{
}
printf("Frequency %u Hz\n", edge_counter_frequency());
#endif
}
}
// Initialise gate timer, and DMA to control the counter
void gate_timer_init(int pin)
{
gate_slice = pwm_gpio_to_slice_num(pin);
io_rw_32 *counter_slice_csr = &pwm_hw->slice[counter_slice].csr;
pwm_set_clkdiv_int_frac(gate_slice, TIMER_PRESCALE, 0);
pwm_set_wrap(gate_slice, TIMER_WRAP/2 - 1);
pwm_set_chan_level(gate_slice, PWM_CHAN_B, TIMER_WRAP/4);
pwm_set_phase_correct(gate_slice, true);
gate_dma_chan = dma_claim_unused_channel(true);
dma_channel_config cfg = dma_channel_get_default_config(gate_dma_chan);
channel_config_set_transfer_data_size(&cfg, DMA_SIZE_32);
channel_config_set_read_increment(&cfg, false);
channel_config_set_dreq(&cfg, pwm_get_dreq(gate_slice));
csr_stopval = *counter_slice_csr;
dma_channel_configure(gate_dma_chan, &cfg, counter_slice_csr, &csr_stopval, 1, false);
pwm_set_enabled(gate_slice, true);
}
// Initialise frequency counter
void freq_counter_init(int pin)
{
assert(pwm_gpio_to_channel(pin) == PWM_CHAN_B);
counter_slice = pwm_gpio_to_slice_num(pin);
gpio_set_function(pin, GPIO_FUNC_PWM);
pwm_config cfg = pwm_get_default_config();
pwm_config_set_clkdiv_mode(&cfg, PWM_DIV_B_RISING);
pwm_config_set_clkdiv(&cfg, 1);
pwm_init(counter_slice, &cfg, false);
}
// Start frequency counter
void freq_counter_start(void)
{
dma_channel_transfer_from_buffer_now(gate_dma_chan, &csr_stopval, 1);
pwm_set_counter(counter_slice, 0);
pwm_set_counter(gate_slice, 0);
counter_lastval = counter_overflow = 0;
pwm_set_mask_enabled((1 << counter_slice) | (1 << gate_slice));
}
// Check for overflow, and check if capture complete
bool freq_counter_value_ready(void)
{
uint n = pwm_get_counter(counter_slice);
if (n < counter_lastval)
counter_overflow++;
counter_lastval = n;
return (!dma_channel_is_busy(gate_dma_chan));
}
// Get counter value
int freq_counter_value(void)
{
while (dma_channel_is_busy(gate_dma_chan)) ;
pwm_set_enabled(gate_slice, false);
return((uint16_t)pwm_get_counter(counter_slice) + counter_overflow*65537);
}
// Get frequency value, return -ve if not ready
int edge_counter_frequency(void)
{
int val = -1;
if (freq_counter_value_ready())
val = freq_counter_value() * SAMPLE_FREQ;
return (val);
}
// Initialise DMA to transfer the edge times
void edge_timer_init(void)
{
timer_dma_chan = dma_claim_unused_channel(true);
dma_channel_config cfg = dma_channel_get_default_config(timer_dma_chan);
channel_config_set_transfer_data_size(&cfg, DMA_SIZE_32);
channel_config_set_read_increment(&cfg, false);
channel_config_set_write_increment(&cfg, true);
channel_config_set_dreq(&cfg, pwm_get_dreq(counter_slice));
dma_channel_configure(timer_dma_chan, &cfg, edge_times, &timer_hw->timerawl, NUM_EDGE_TIMES, false);
pwm_set_wrap(counter_slice, 0);
}
// Start DMA to record pulse times
void edge_timer_start(void)
{
dma_channel_transfer_to_buffer_now(timer_dma_chan, edge_times, NUM_EDGE_TIMES);
pwm_set_enabled(counter_slice, true);
}
// Get average of the edge times
int edge_timer_value(void)
{
uint i=1, n;
int total=0;
dma_channel_abort(timer_dma_chan);
pwm_set_enabled(counter_slice, false);
while (i<NUM_EDGE_TIMES && edge_times[i])
{
n = edge_times[i] - edge_times[i-1];
total += n;
i++;
}
return(i>1 ? total / (i - 1) : 0);
}
// Get frequency value from edge timer
float edge_timer_frequency(void)
{
int val = edge_timer_value();
return(val ? 1e6 / val : 0);
}
// Delay given number of milliseconds
void msdelay(int msec)
{
uint ticks;
if (msec)
{
ustimeout(&ticks, 0);
while (!ustimeout(&ticks, msec*1000)) ;
}
}
// Return non-zero if timeout
bool ustimeout(uint *tickp, uint usec)
{
uint t = time_us_32(), dt = t - *tickp;
if (usec == 0 || dt >= usec)
{
*tickp = t;
return (1);
}
return (0);
}
// EOF