scpi-dmm: Added minimal support for HP34401A (PR #36)

src/hardware/scpi-dmm/api.c

@@ -49,6 +49,34 @@ static const struct scpi_command cmdset_agilent[] = {
 	ALL_ZERO,
 };
 
+/*
+ * cmdset_hp is used for the 34401A, which was added to this code after the 
+ * 34405A and 34465A. It differs in starting the measurement with INIT: using
+ * MEAS without a trailing '?' (as used for the 34405A) is not valid for the
+ * 34401A and gives an error. 
+ * I'm surprised the same instruction sequence doesn't work and INIT may 
+ * work for both, but I don't have the others to re-test. 
+ *
+ * On the 34401A, 
+ *  MEAS <optional parameters> ? configures, arms, triggers and waits 
+ *       for a reading
+ *  CONF <parameters> configures
+ *  INIT prepares for triggering (trigger mode is not set, assumed 
+ *       internal - external might time out)
+ *  *OPC waits for completion, and
+ *  READ? retrieves the result
+ */
+static const struct scpi_command cmdset_hp[] = {
+	{ DMM_CMD_SETUP_REMOTE, "\n", },
+	{ DMM_CMD_SETUP_FUNC, "CONF:%s", },
+	{ DMM_CMD_QUERY_FUNC, "CONF?", },
+	{ DMM_CMD_START_ACQ, "INIT", },
+	{ DMM_CMD_STOP_ACQ, "ABORT", },
+	{ DMM_CMD_QUERY_VALUE, "READ?", },
+	{ DMM_CMD_QUERY_PREC, "CONF?", },
+	ALL_ZERO,
+};
+
 static const struct mqopt_item mqopts_agilent_34405a[] = {
 	{ SR_MQ_VOLTAGE, SR_MQFLAG_DC, "VOLT:DC", "VOLT ", NO_DFLT_PREC, },
 	{ SR_MQ_VOLTAGE, SR_MQFLAG_AC, "VOLT:AC", "VOLT:AC ", NO_DFLT_PREC, },
@@ -62,18 +90,41 @@ static const struct mqopt_item mqopts_agilent_34405a[] = {
 	{ SR_MQ_FREQUENCY, 0, "FREQ", "FREQ ", NO_DFLT_PREC, },
 };
 
+static const struct mqopt_item mqopts_agilent_34401a[] = {
+	{ SR_MQ_VOLTAGE, SR_MQFLAG_DC, "VOLT:DC", "VOLT ", NO_DFLT_PREC, },
+	{ SR_MQ_VOLTAGE, SR_MQFLAG_AC, "VOLT:AC", "VOLT:AC ", NO_DFLT_PREC, },
+	{ SR_MQ_CURRENT, SR_MQFLAG_DC, "CURR:DC", "CURR ", NO_DFLT_PREC, },
+	{ SR_MQ_CURRENT, SR_MQFLAG_AC, "CURR:AC", "CURR:AC ", NO_DFLT_PREC, },
+	{ SR_MQ_RESISTANCE, 0, "RES", "RES ", NO_DFLT_PREC, },
+	{ SR_MQ_RESISTANCE, SR_MQFLAG_FOUR_WIRE, "FRES", "FRES ", NO_DFLT_PREC, },
+	{ SR_MQ_CONTINUITY, 0, "CONT", "CONT", -1, },
+	{ SR_MQ_VOLTAGE, SR_MQFLAG_DC | SR_MQFLAG_DIODE, "DIOD", "DIOD", -4, },
+	{ SR_MQ_FREQUENCY, 0, "FREQ", "FREQ ", NO_DFLT_PREC, },
+	{ SR_MQ_TIME, 0, "PER", "PER ", NO_DFLT_PREC, },
+};
+
 SR_PRIV const struct scpi_dmm_model models[] = {
 	{
 		"Agilent", "34405A",
 		1, 5, cmdset_agilent, ARRAY_AND_SIZE(mqopts_agilent_34405a),
 		scpi_dmm_get_meas_agilent,
 		ARRAY_AND_SIZE(devopts_generic),
+                0,
 	},
 	{
 		"Keysight", "34465A",
 		1, 5, cmdset_agilent, ARRAY_AND_SIZE(mqopts_agilent_34405a),
 		scpi_dmm_get_meas_agilent,
 		ARRAY_AND_SIZE(devopts_generic),
+                0,
+	},
+	{
+		"HP", "34401A",
+		1, 6, cmdset_hp, ARRAY_AND_SIZE(mqopts_agilent_34401a),
+		scpi_dmm_get_meas_agilent,
+		ARRAY_AND_SIZE(devopts_generic),
+		/* 34401A: typ. 1020ms for AC readings (default is 1000ms). */
+		1000 * 1500, 
 	},
 };
 
@@ -129,7 +180,8 @@ static struct sr_dev_inst *probe_device(struct sr_scpi_dev_inst *scpi)
 	sdi->driver = &scpi_dmm_driver_info;
 	sdi->inst_type = SR_INST_SCPI;
 	sr_scpi_hw_info_free(hw_info);
-
+        if (model->read_timeout_us)  /* non-default read timeout */
+		scpi->read_timeout_us = model->read_timeout_us;
 	devc = g_malloc0(sizeof(*devc));
 	sdi->priv = devc;
 	devc->num_channels = model->num_channels;

src/hardware/scpi-dmm/protocol.c

@@ -386,6 +386,9 @@ SR_PRIV int scpi_dmm_get_meas_agilent(const struct sr_dev_inst *sdi, size_t ch)
 	case SR_MQ_FREQUENCY:
 		unit = SR_UNIT_HERTZ;
 		break;
+	case SR_MQ_TIME:
+		unit = SR_UNIT_SECOND;
+		break;
 	default:
 		return SR_ERR_NA;
 	}

src/hardware/scpi-dmm/protocol.h

@@ -62,6 +62,7 @@ struct scpi_dmm_model {
 	int (*get_measurement)(const struct sr_dev_inst *sdi, size_t ch);
 	const uint32_t *devopts;
 	size_t devopts_size;
+	unsigned int read_timeout_us; /* If zero, use default from src/scpi/scpi.c. */
 };
 
 struct dev_context {