SPI Examples

examples/spi.cpp

@@ -0,0 +1,167 @@
+#include <chrono>
+#include <thread>
+#include <csignal>
+#include <iostream>
+#include <cstring>
+#include <fcntl.h>
+#include <cstdint>
+#include <sys/ioctl.h>
+#include <linux/spi/spidev.h>
+#include <pulse/simple.h>
+#include <pulse/error.h>
+
+using namespace std;
+using namespace chrono;
+
+#define SPI_DEVICE "/dev/spidev0.0"
+#define SPI_SPEED_HZ 4000000
+#define ADC_RATE 16000
+#define BLOCK_SIZE 4096
+#define ALPHA 1
+#define CORR_POWER 0.1
+
+volatile bool active = true;
+int spi_fd = -1;
+pa_simple *pa_handle = nullptr;
+
+double filtered = 0.0;
+double correction = 0.0;
+
+uint8_t tx[2] = {0, 0}, rx[2] = {0, 0};
+
+struct spi_ioc_transfer tr = {
+    .tx_buf = (unsigned long)tx,
+    .rx_buf = (unsigned long)rx,
+    .len = 2,
+    .speed_hz = SPI_SPEED_HZ,
+    .bits_per_word = 8};
+
+void handler(int sig)
+{
+    active = false;
+}
+
+void init_pulse()
+{
+    pa_sample_spec ss = {
+        .format = PA_SAMPLE_S16LE,
+        .rate = ADC_RATE,
+        .channels = 1};
+
+    pa_buffer_attr ba = {
+        .maxlength = BLOCK_SIZE * sizeof(int16_t) * 4,
+        .tlength = BLOCK_SIZE * sizeof(int16_t),
+        .prebuf = BLOCK_SIZE * sizeof(int16_t) * 2,
+        .minreq = BLOCK_SIZE * sizeof(int16_t)};
+
+    int error;
+    pa_handle = pa_simple_new(nullptr, "ADS8320", PA_STREAM_PLAYBACK, nullptr, "ADC", &ss, nullptr, &ba, &error);
+    if (!pa_handle)
+    {
+        std::cerr << "PulseAudio error: " << pa_strerror(error) << std::endl;
+        exit(1);
+    }
+}
+
+void spi_init()
+{
+    spi_fd = open(SPI_DEVICE, O_RDWR);
+    if (spi_fd < 0)
+    {
+        std::cerr << "SPI error: " << strerror(errno) << std::endl;
+        exit(1);
+    }
+
+    uint8_t mode = SPI_MODE_0;
+    uint8_t bits = 8;
+    uint32_t speed = SPI_SPEED_HZ;
+    if (ioctl(spi_fd, SPI_IOC_WR_MODE, &mode) < 0)
+    {
+        std::cerr << "SPI mode error: " << strerror(errno) << std::endl;
+        exit(1);
+    }
+    if (ioctl(spi_fd, SPI_IOC_WR_BITS_PER_WORD, &bits) < 0)
+    {
+        std::cerr << "SPI bits error: " << strerror(errno) << std::endl;
+        exit(1);
+    }
+    if (ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed) < 0)
+    {
+        std::cerr << "SPI speed error: " << strerror(errno) << std::endl;
+        exit(1);
+    }
+}
+
+int16_t spi_read()
+{
+    ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr);
+
+    uint32_t raw = (rx[0] << 11) | ((rx[1]) << 1);
+    return static_cast<int16_t>(raw+INT16_MIN);
+}
+
+int main()
+{
+    signal(SIGINT, handler);
+    signal(SIGTERM, handler);
+
+    spi_init();
+    init_pulse();
+
+    steady_clock::time_point next = steady_clock::now();
+    const duration<double> step(1.0 / ADC_RATE);
+    const steady_clock::duration step_duration = duration_cast<steady_clock::duration>(step);
+
+    int16_t buffer[BLOCK_SIZE];
+    while (active)
+    {
+        int min_val = INT16_MAX;
+        int max_val = INT16_MIN;
+        double sum = 0.0;
+
+        auto block_start = steady_clock::now();
+        for (int i = 0; i < BLOCK_SIZE && active; i++)
+        {
+            steady_clock::time_point now = steady_clock::now();
+            if (now < next)
+                std::this_thread::sleep_until(next);
+
+            int16_t sample = spi_read();
+            //filtered = ALPHA * sample + (1 - ALPHA) * filtered;
+            buffer[i] = sample;
+
+            if(sample<min_val)
+                min_val=sample;
+            if(sample>max_val)
+                max_val=sample;
+
+            sum += sample;
+            next += step_duration;
+        }
+
+        int error;
+        if (pa_simple_write(pa_handle, buffer, BLOCK_SIZE * sizeof(int16_t), &error) < 0) {
+            std::cerr << "Pulse write error: " << pa_strerror(error) << std::endl;
+        }
+
+        double block_time = duration_cast<duration<double>>(steady_clock::now() - block_start).count();
+
+        double avg = sum / BLOCK_SIZE;
+        correction = correction + avg * CORR_POWER;
+
+        double voltage = avg / 32768.0 * 5;
+
+        printf("Block: %.4fs (expected: %.4fs) | min=%6d max=%6d corr=%8.1f avg=%8.1f → %.3fV \n",
+               block_time, BLOCK_SIZE * 1.0 / ADC_RATE, min_val, max_val, correction, avg, voltage);
+    }
+
+    if (pa_handle)
+    {
+        pa_simple_drain(pa_handle, nullptr);
+        pa_simple_free(pa_handle);
+    }
+
+    if (spi_fd >= 0)
+        close(spi_fd);
+}
+