Backport recent changes from mainline.

[libsigrok.git] / src / output / vcd.c

diff --git a/src/output/vcd.c b/src/output/vcd.c
index f90db498e5710d1d595bfab3c5b27818c7b2d202..3de3dcde37b3a044679ed745e498433c987aa047 100644 (file)
--- a/src/output/vcd.c
+++ b/src/output/vcd.c
@@ -31,7 +31,7 @@ struct context {
        int num_enabled_channels;
        uint8_t *prevsample;
        gboolean header_done;
-       int period;
+       uint64_t period;
        int *channel_index;
        uint64_t samplerate;
        uint64_t samplecount;
@@ -78,6 +78,38 @@ static int init(struct sr_output *o, GHashTable *options)
        return SR_OK;
 }
 
+/*
+ * VCD can only handle 1/10/100 factors in the s to fs range. Find a
+ * suitable timescale which satisfies this resolution constraint, yet
+ * won't result in excessive overhead.
+ */
+static uint64_t get_timescale_freq(uint64_t samplerate)
+{
+       uint64_t timescale;
+       int max_up_scale;
+
+       /* Go to the next full decade. */
+       timescale = 1;
+       while (timescale < samplerate) {
+               timescale *= 10;
+       }
+
+       /*
+        * Avoid loss of precision, go up a few more decades when needed.
+        * For example switch to 10GHz timescale when samplerate is 400MHz.
+        * Stop after at most factor 100 to not loop endlessly for odd
+        * samplerates, yet provide good enough accuracy.
+        */
+       max_up_scale = 2;
+       while (max_up_scale--) {
+               if (timescale / samplerate * samplerate == timescale)
+                       break;
+               timescale *= 10;
+       }
+
+       return timescale;
+}
+
 static GString *gen_header(const struct sr_output *o)
 {
        struct context *ctx;
@@ -102,7 +134,7 @@ static GString *gen_header(const struct sr_output *o)
 
        /* generator */
        g_string_append_printf(header, "$version %s %s $end\n",
-                       PACKAGE_NAME, SR_PACKAGE_VERSION_STRING);
+                       PACKAGE_NAME, sr_package_version_string_get());
        g_string_append_printf(header, "$comment\n  Acquisition with "
                        "%d/%d channels", ctx->num_enabled_channels, num_channels);
 
@@ -121,13 +153,7 @@ static GString *gen_header(const struct sr_output *o)
        g_string_append_printf(header, "\n$end\n");
 
        /* timescale */
-       /* VCD can only handle 1/10/100 (s - fs), so scale up first */
-       if (ctx->samplerate > SR_MHZ(1))
-               ctx->period = SR_GHZ(1);
-       else if (ctx->samplerate > SR_KHZ(1))
-               ctx->period = SR_MHZ(1);
-       else
-               ctx->period = SR_KHZ(1);
+       ctx->period = get_timescale_freq(ctx->samplerate);
        frequency_s = sr_period_string(1, ctx->period);
        g_string_append_printf(header, "$timescale %s $end\n", frequency_s);
        g_free(frequency_s);