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 e4346e5db6d3fef19360e24367f291dd45f7b789..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) {
@@ -417,43 +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;
-       unsigned int offset = 0;
+       gint64 laststart, now;
+       unsigned int offset;
        int space;
 
-       if (command)
+       /* 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();
                }
-               offset += len;
-               g_string_set_size(response, offset);
-               elapsed_ms = (g_get_monotonic_time() - laststart) / 1000;
-               if (elapsed_ms >= scpi->read_timeout_ms) {
+
+               now = g_get_monotonic_time();
+
+               if (len > 0) {
+                       laststart = now;
+                       offset += len;
+                       g_string_set_size(response, offset);
+               } 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;
                }
        }
 
@@ -723,6 +731,7 @@ SR_PRIV int sr_scpi_get_uint8v(struct sr_scpi_dev_inst *scpi,
 
        return ret;
 }
+
 /**
  * Send a SCPI command, read the reply, parse it as binary data with a
  * "definite length block" header and store the as an result in scpi_response.
@@ -741,62 +750,80 @@ SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
 {
        int ret;
        GString* response;
-
-       char buf[10] = { 0 };
+       char buf[10];
        long llen;
        long datalen;
 
+       /*
+        * Assume an initial maximum length, optionally gets adjusted below.
+        * Prepare a NULL return value for when error paths will be taken.
+        */
        response = g_string_sized_new(1024);
        *scpi_response = NULL;
 
+       /* Get (the first chunk of) the response. */
        ret = sr_scpi_get_data(scpi, command, &response);
        if (ret != SR_OK) {
                g_string_free(response, TRUE);
                return ret;
        }
 
+       /*
+        * SCPI protocol data blocks are preceeded with a length spec.
+        * The length spec consists of a '#' marker, one digit which
+        * specifies the character count of the length spec, and the
+        * respective number of characters which specify the data block's
+        * length. Raw data bytes follow (thus one must no longer assume
+        * that the received input stream would be an ASCIIZ string).
+        *
+        * Get the data block length, and strip off the length spec from
+        * the input buffer, leaving just the data bytes.
+        */
        if (response->str[0] != '#') {
                g_string_free(response, TRUE);
                return SR_ERR_DATA;
        }
-
        buf[0] = response->str[1];
+       buf[1] = '\0';
        ret = sr_atol(buf, &llen);
        if ((ret != SR_OK) || (llen == 0)) {
                g_string_free(response, TRUE);
                return ret;
        }
-
        memcpy(buf, &response->str[2], llen);
+       buf[llen] = '\0';
        ret = sr_atol(buf, &datalen);
        if ((ret != SR_OK) || (datalen == 0)) {
                g_string_free(response, TRUE);
                return ret;
        }
-
-       // strip header
        g_string_erase(response, 0, 2 + llen);
 
+       /*
+        * If the initially assumed length does not cover the data block
+        * length, then re-allocate the buffer size to the now known
+        * length, and keep reading more chunks of response data.
+        */
        if (response->len < (unsigned long)(datalen)) {
                int oldlen = response->len;
                g_string_set_size(response, datalen);
                g_string_set_size(response, oldlen);
        }
-
        while (response->len < (unsigned long)(datalen)) {
-               if (sr_scpi_get_data(scpi, NULL, &response) != SR_OK) {
+               ret = sr_scpi_get_data(scpi, NULL, &response);
+               if (ret != SR_OK) {
                        g_string_free(response, TRUE);
                        return ret;
                }
        }
 
+       /* Convert received data to byte array. */
        *scpi_response = g_byte_array_new_take(
                (guint8*)g_string_free(response, FALSE), datalen);
 
        return ret;
 }
 
-
 /**
  * Send the *IDN? SCPI command, receive the reply, parse it and store the
  * reply as a sr_scpi_hw_info structure in the supplied scpi_response pointer.