hp-3478a: Check via GPIB serial poll if new data is available.

[libsigrok.git] / src / hardware / hp-3478a / protocol.c

diff --git a/src/hardware/hp-3478a/protocol.c b/src/hardware/hp-3478a/protocol.c
index 3ddce5884aa1bddd72a199f4823bae3e2cde5f2c..6767bf0a03b4e7ff8b1b4b260c05a3fbe7abdc16 100644 (file)
--- a/src/hardware/hp-3478a/protocol.c
+++ b/src/hardware/hp-3478a/protocol.c
@@ -406,6 +406,7 @@ SR_PRIV int hp_3478a_receive_data(int fd, int revents, void *cb_data)
        struct sr_scpi_dev_inst *scpi;
        struct sr_dev_inst *sdi;
        struct dev_context *devc;
+       char status_register;
 
        (void)fd;
        (void)revents;
@@ -416,18 +417,28 @@ SR_PRIV int hp_3478a_receive_data(int fd, int revents, void *cb_data)
        scpi = sdi->conn;
 
        /*
-        * This is necessary to get the actual range for the encoding digits.
-        * When SPoll is implemmented, this can be done via SPoll.
+        * TODO: Wait for SRQ from the DMM when a new measurement is available.
+        *       For now, we don't wait for a SRQ, but just do a SPoll and
+        *       check the Data Ready bit (0x01).
+        *       This is necessary, because (1) reading a value will block the
+        *       bus until a measurement is available and (2) when switching
+        *       ranges, there could be a timeout.
         */
-       if (hp_3478a_get_status_bytes(sdi) != SR_OK)
+       if (sr_scpi_gpib_spoll(scpi, &status_register) != SR_OK)
+               return FALSE;
+       if (!(((uint8_t)status_register) & 0x01))
+               return TRUE;
+
+       /* Get a reading from the DMM. */
+       if (sr_scpi_get_double(scpi, NULL, &devc->measurement) != SR_OK)
                return FALSE;
 
        /*
-        * TODO: Implement GPIB-SPoll, to get notified by a SRQ when a new
-        *       measurement is available. This is necessary, because when
-        *       switching ranges, there could be a timeout.
+        * This is necessary to get the actual range for the encoding digits.
+        * Must be called after reading the value, because it resets the
+        * status register!
         */
-       if (sr_scpi_get_double(scpi, NULL, &devc->measurement) != SR_OK)
+       if (hp_3478a_get_status_bytes(sdi) != SR_OK)
                return FALSE;
 
        acq_send_measurement(sdi);