baylibre-acme: Use timerfd instead of a fake pipe.

Currently baylibre-acme uses a fake pipe as the input channel required by
libsigrok API and calls sleep() in the data acquisition callback to create
intervals between measurements.

Switch to a more elegant approach: use Linux' timerfd and set a periodic
timer equal to the sampling rate. Then read the data every time the timer
expires.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

src/hardware/baylibre-acme/api.c

@@ -18,6 +18,8 @@
  */
 
 #include "protocol.h"
+#include <time.h>
+#include <sys/timerfd.h>
 
 SR_PRIV struct sr_dev_driver baylibre_acme_driver_info;
 
@@ -349,6 +351,10 @@ static int dev_acquisition_open(const struct sr_dev_inst *sdi)
 static int dev_acquisition_start(const struct sr_dev_inst *sdi, void *cb_data)
 {
 	struct dev_context *devc;
+	struct itimerspec tspec = {
+		.it_interval = { 0, 0 },
+		.it_value = { 0, 0 }
+	};
 
 	(void)cb_data;
 
@@ -360,19 +366,30 @@ static int dev_acquisition_start(const struct sr_dev_inst *sdi, void *cb_data)
 
 	devc = sdi->priv;
 	devc->samples_read = 0;
-
-	if (pipe(devc->pipe_fds)) {
-		sr_err("Error setting up pipe");
+	devc->samples_missed = 0;
+	devc->timer_fd = timerfd_create(CLOCK_MONOTONIC, 0);
+	if (devc->timer_fd < 0) {
+		sr_err("Error creating timer fd");
 		return SR_ERR;
 	}
 
-	devc->channel = g_io_channel_unix_new(devc->pipe_fds[0]);
+	tspec.it_interval.tv_sec = 0;
+	tspec.it_interval.tv_nsec = (1000000000L / devc->samplerate);
+	tspec.it_value = tspec.it_interval;
+
+	if (timerfd_settime(devc->timer_fd, 0, &tspec, NULL)) {
+		sr_err("Failed to set timer");
+		close(devc->timer_fd);
+		return SR_ERR;
+	}
+
+	devc->channel = g_io_channel_unix_new(devc->timer_fd);
 	g_io_channel_set_flags(devc->channel, G_IO_FLAG_NONBLOCK, NULL);
 	g_io_channel_set_encoding(devc->channel, NULL, NULL);
 	g_io_channel_set_buffered(devc->channel, FALSE);
 
 	sr_session_source_add_channel(sdi->session, devc->channel,
-		G_IO_IN | G_IO_ERR, 1, bl_acme_receive_data, (void *)sdi);
+		G_IO_IN | G_IO_ERR, 1000, bl_acme_receive_data, (void *)sdi);
 
 	/* Send header packet to the session bus. */
 	std_session_send_df_header(sdi, LOG_PREFIX);
@@ -398,11 +415,15 @@ static int dev_acquisition_stop(struct sr_dev_inst *sdi, void *cb_data)
 	g_io_channel_shutdown(devc->channel, FALSE, NULL);
 	g_io_channel_unref(devc->channel);
 	devc->channel = NULL;
+	close(devc->timer_fd);
 
 	/* Send last packet. */
 	packet.type = SR_DF_END;
 	sr_session_send(sdi, &packet);
 
+	if (devc->samples_missed > 0)
+		sr_warn("%d samples missed", devc->samples_missed);
+
 	return SR_OK;
 }
 

src/hardware/baylibre-acme/protocol.c

@@ -560,8 +560,8 @@ SR_PRIV void bl_acme_close_channel(struct sr_channel *ch)
 
 SR_PRIV int bl_acme_receive_data(int fd, int revents, void *cb_data)
 {
-	uint32_t cur_time, elapsed_time, diff_time;
-	int64_t time_to_sleep;
+	uint32_t cur_time, elapsed_time;
+	uint64_t nrexpiration;
 	struct sr_datafeed_packet packet, framep;
 	struct sr_datafeed_analog analog;
 	struct sr_dev_inst *sdi;
@@ -586,17 +586,18 @@ SR_PRIV int bl_acme_receive_data(int fd, int revents, void *cb_data)
 	memset(&analog, 0, sizeof(struct sr_datafeed_analog));
 	analog.data = &valf;
 
-	/*
-	 * Reading from sysfs takes some time - try to keep up with samplerate.
-	 */
-	if (devc->samples_read) {
-		cur_time = g_get_monotonic_time();
-		diff_time = cur_time - devc->last_sample_fin;
-		time_to_sleep = G_USEC_PER_SEC / devc->samplerate - diff_time;
-		if (time_to_sleep > 0)
-			g_usleep(time_to_sleep);
+	if (read(devc->timer_fd, &nrexpiration, sizeof(nrexpiration)) < 0) {
+		sr_warn("Failed to read timer information");
+		return TRUE;
 	}
 
+	/*
+	 * We were not able to process the previous timer expiration, we are
+	 * overloaded.
+	 */
+	if (nrexpiration > 1)
+		devc->samples_missed += nrexpiration - 1;
+
 	framep.type = SR_DF_FRAME_BEGIN;
 	sr_session_send(cb_data, &framep);
 

src/hardware/baylibre-acme/protocol.h

@@ -65,9 +65,10 @@ struct dev_context {
 
 	uint32_t num_channels;
 	uint64_t samples_read;
+	uint64_t samples_missed;
 	int64_t start_time;
 	int64_t last_sample_fin;
-	int pipe_fds[2];
+	int timer_fd;
 	GIOChannel *channel;
 };