baylibre-acme: Add a workaround for slow data acquisition.

[libsigrok.git] / src / hardware / baylibre-acme / protocol.c

diff --git a/src/hardware/baylibre-acme/protocol.c b/src/hardware/baylibre-acme/protocol.c
index 5552ff565bbbad12a2feee85f56e5d42c096e516..8e730f15d0f26e5933512f86fa7da4cdddc3d4e6 100644 (file)
--- a/src/hardware/baylibre-acme/protocol.c
+++ b/src/hardware/baylibre-acme/protocol.c
@@ -34,6 +34,7 @@ struct channel_group_priv {
 struct channel_priv {
        int ch_type;
        int fd;
+       float val;
        struct channel_group_priv *probe;
 };
 
@@ -566,9 +567,10 @@ SR_PRIV int bl_acme_receive_data(int fd, int revents, void *cb_data)
        struct sr_datafeed_analog analog;
        struct sr_dev_inst *sdi;
        struct sr_channel *ch;
+       struct channel_priv *chp;
        struct dev_context *devc;
        GSList *chl, chonly;
-       float valf;
+       unsigned i;
 
        (void)fd;
        (void)revents;
@@ -584,7 +586,6 @@ SR_PRIV int bl_acme_receive_data(int fd, int revents, void *cb_data)
        packet.type = SR_DF_ANALOG;
        packet.payload = &analog;
        memset(&analog, 0, sizeof(struct sr_datafeed_analog));
-       analog.data = &valf;
 
        if (read(devc->timer_fd, &nrexpiration, sizeof(nrexpiration)) < 0) {
                sr_warn("Failed to read timer information");
@@ -598,31 +599,53 @@ SR_PRIV int bl_acme_receive_data(int fd, int revents, void *cb_data)
        if (nrexpiration > 1)
                devc->samples_missed += nrexpiration - 1;
 
-       framep.type = SR_DF_FRAME_BEGIN;
-       sr_session_send(cb_data, &framep);
-
        /*
-        * Due to different units used in each channel we're sending
-        * samples one-by-one.
+        * XXX This is a nasty workaround...
+        *
+        * At high sampling rates and maximum channels we are not able to
+        * acquire samples fast enough, even though frontends still think
+        * that samples arrive on time. This causes shifts in frontend
+        * plots.
+        *
+        * To compensate for the delay we check if any clock events were
+        * missed and - if so - don't really read the next value, but send
+        * the same sample as fast as possible. We do it until we are back
+        * on schedule.
+        *
+        * At high sampling rate this doesn't seem to visibly reduce the
+        * accuracy.
         */
-       for (chl = sdi->channels; chl; chl = chl->next) {
-               ch = chl->data;
-               if (!ch->enabled)
-                       continue;
-               chonly.next = NULL;
-               chonly.data = ch;
-               analog.channels = &chonly;
-               analog.num_samples = 1;
-               analog.mq = channel_to_mq(chl->data);
-               analog.unit = channel_to_unit(ch);
-
-               valf = read_sample(ch);
-
-               sr_session_send(cb_data, &packet);
-       }
+       for (i = 0; i < nrexpiration; i++) {
+               framep.type = SR_DF_FRAME_BEGIN;
+               sr_session_send(cb_data, &framep);
+
+               /*
+                * Due to different units used in each channel we're sending
+                * samples one-by-one.
+                */
+               for (chl = sdi->channels; chl; chl = chl->next) {
+                       ch = chl->data;
+                       chp = ch->priv;
 
-       framep.type = SR_DF_FRAME_END;
-       sr_session_send(cb_data, &framep);
+                       if (!ch->enabled)
+                               continue;
+                       chonly.next = NULL;
+                       chonly.data = ch;
+                       analog.channels = &chonly;
+                       analog.num_samples = 1;
+                       analog.mq = channel_to_mq(chl->data);
+                       analog.unit = channel_to_unit(ch);
+
+                       if (i < 1)
+                               chp->val = read_sample(ch);
+
+                       analog.data = &chp->val;
+                       sr_session_send(cb_data, &packet);
+               }
+
+               framep.type = SR_DF_FRAME_END;
+               sr_session_send(cb_data, &framep);
+       }
 
        devc->samples_read++;
        if (devc->limit_samples > 0 &&