3 files changed, 101 insertions(+), 0 deletions(-)

A .gitignore
A Makefile
A geiger.c

@@ 1,2 @@
+*.o
+geiger

@@ 1,18 @@
+CC = clang
+CFLAGS = -std=c99 -Wall -D_POSIX_C_SOURCE=200809L
+LDFLAGS = -lpthread -lasound
+SOURCES = $(wildcard *.c)
+OBJECTS = $(SOURCES:.c=.o)
+EXECUTABLE = geiger
+
+all: $(EXECUTABLE)
+
+%.o: %.c %.h
+	$(CC) -c $(CFLAGS) $< -o $@
+
+$(EXECUTABLE): $(OBJECTS)
+	$(CC) $(CFLAGS) $(LDFLAGS) $^ -o $@
+
+.PHONY: clean all
+clean:
+	rm -f *.o $(EXECUTABLE)

@@ 1,81 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <alsa/asoundlib.h>
+
+char stop = 0;
+char decay = 0;
+
+void* worker(void *z){
+    // mostly lifted from https://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm__min_8c-example.html
+    static char *device = "default";
+
+    unsigned char click[16];
+    unsigned char blank[16];
+
+    int err;
+    unsigned int i;
+    snd_pcm_t *handle;
+    snd_pcm_sframes_t frames;
+
+    for (i = 0; i < sizeof(click); i++){
+        click[i] = 0;
+        blank[i] = 0;
+    }
+    click[0] = 250;
+
+    if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
+        fprintf(stderr, "Playback open error: %s\n", snd_strerror(err));
+        exit(EXIT_FAILURE);
+    }
+    if ((err = snd_pcm_set_params(handle,
+                                  SND_PCM_FORMAT_U8,
+                                  SND_PCM_ACCESS_RW_INTERLEAVED,
+                                  1,
+                                  8000,
+                                  1,
+                                  125)) < 0) {
+        fprintf(stderr, "Playback open error: %s\n", snd_strerror(err));
+        exit(EXIT_FAILURE);
+    }
+
+    while (!stop) {
+        if (decay) {
+            frames = snd_pcm_writei(handle, click, sizeof(click));
+            decay = 0;
+        }
+        else
+            frames = snd_pcm_writei(handle, blank, sizeof(click));
+        if (frames < 0)
+            frames = snd_pcm_recover(handle, frames, 0);
+            if (frames < 0) {
+                fprintf(stderr, "snd_pcm_writei failed: %s\n", snd_strerror(err));
+                break;
+            }
+            if (frames > 0 && frames < (long)sizeof(click))
+                fprintf(stderr, "Short write (expected %li, wrote %li)\n", (long)sizeof(click), frames);
+    }
+
+    snd_pcm_close(handle);
+    return 0;
+}
+
+int main(){
+    pthread_t worker_thread;
+    int rc = pthread_create(&worker_thread, NULL, worker, (void *)NULL);
+    if (rc) {
+        fprintf(stderr, "Whoops!\n");
+        return -1;
+    }
+    for (;;){
+        char input = getchar();
+        if (input != 10){
+            break;
+        }
+        decay = 1;
+    }
+    stop = 1;
+    fprintf(stderr, "Stopping: %d\n", stop);
+    pthread_join(worker_thread, NULL);
+    return 0;
+}