scpi: Query current time just once, use microseconds for timeout

[libsigrok.git] / src / scpi / scpi.c

diff --git a/src/scpi/scpi.c b/src/scpi/scpi.c
index f743f64d6b75d5f072cc2e8af8e8195e5b881113..f6865c37dc846d809a016b0627cb4fb44630813d 100644 (file)
--- a/src/scpi/scpi.c
+++ b/src/scpi/scpi.c
@@ -190,7 +190,7 @@ SR_PRIV struct sr_scpi_dev_inst *scpi_dev_inst_new(struct drv_context *drvc,
                        scpi = g_malloc(sizeof(*scpi));
                        *scpi = *scpi_dev;
                        scpi->priv = g_malloc0(scpi->priv_size);
-                       scpi->read_timeout_ms = 1000;
+                       scpi->read_timeout_us = 1000 * 1000;
                        params = g_strsplit(resource, "/", 0);
                        if (scpi->dev_inst_new(scpi->priv, drvc, resource,
                                               params, serialcomm) != SR_OK) {
@@ -417,44 +417,51 @@ SR_PRIV int sr_scpi_get_data(struct sr_scpi_dev_inst *scpi,
 {
        int len;
        GString *response;
-       gint64 laststart;
-       unsigned int elapsed_ms;
+       gint64 laststart, now;
        unsigned int offset;
        int space;
 
+       /* Optionally send caller provided command. */
        if (command) {
                if (sr_scpi_send(scpi, command) != SR_OK)
                        return SR_ERR;
        }
 
+       /* Initiate SCPI read operation. */
        if (sr_scpi_read_begin(scpi) != SR_OK)
                return SR_ERR;
 
+       /* Keep reading until completion or until timeout. */
        laststart = g_get_monotonic_time();
 
        response = *scpi_response;
-
        offset = response->len;
 
        while (!sr_scpi_read_complete(scpi)) {
+               /* Resize the buffer when free space drops below a threshold. */
                space = response->allocated_len - response->len;
                if (space < 128) {
                        g_string_set_size(response, response->len + 1024);
+                       g_string_set_size(response, offset);
                        space = response->allocated_len - response->len;
                }
+               /* Read another chunk of the response. */
                len = sr_scpi_read_data(scpi, &response->str[offset], space);
                if (len < 0) {
                        sr_err("Incompletely read SCPI response.");
                        return SR_ERR;
-               } else if (len > 0) {
-                       laststart = g_get_monotonic_time();
+               }
+
+               now = g_get_monotonic_time();
+
+               if (len > 0) {
+                       laststart = now;
                        offset += len;
                        g_string_set_size(response, offset);
-               }
-               elapsed_ms = (g_get_monotonic_time() - laststart) / 1000;
-               if (elapsed_ms >= scpi->read_timeout_ms) {
+               } else if ((now - laststart) >= scpi->read_timeout_us) {
+                       /* Quit reading after a period of time without receiving data. */
                        sr_err("Timed out waiting for SCPI response.");
-                       return SR_ERR;
+                       return SR_ERR_TIMEOUT;
                }
        }