When performing a Comedi read instruction or setting up an asynchronous
command on the AI subdevice, clear any stale data on the A/D registers
by waiting for the Status register's BUSY bit to clear (if set) and then
if the FINISH or ERR bit is set, reading the A/D Data register twice to
clear the stale data.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
drivers/staging/comedi/drivers/dt2814.c | 39 +++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/drivers/staging/comedi/drivers/dt2814.c b/drivers/staging/comedi/drivers/dt2814.c
index bd329d7b4893..7e73aa094eea 100644
--- a/drivers/staging/comedi/drivers/dt2814.c
+++ b/drivers/staging/comedi/drivers/dt2814.c
@@ -52,6 +52,43 @@ struct dt2814_private {
#define DT2814_TIMEOUT 10
#define DT2814_MAX_SPEED 100000 /* Arbitrary 10 khz limit */
+static int dt2814_ai_notbusy(struct comedi_device *dev,
+ struct comedi_subdevice *s,
+ struct comedi_insn *insn,
+ unsigned long context)
+{
+ unsigned int status;
+
+ status = inb(dev->iobase + DT2814_CSR);
+ if (context)
+ *(unsigned int *)context = status;
+ if (status & DT2814_BUSY)
+ return -EBUSY;
+ return 0;
+}
+
+static int dt2814_ai_clear(struct comedi_device *dev)
+{
+ unsigned int status = 0;
+ int ret;
+
+ /* Wait until not busy and get status register value. */
+ ret = comedi_timeout(dev, NULL, NULL, dt2814_ai_notbusy,
+ (unsigned long)&status);
+ if (ret)
+ return ret;
+
+ if (status & (DT2814_FINISH | DT2814_ERR)) {
+ /*
+ * There unread data, or the error flag is set.
+ * Read the data register twice to clear the condition.
+ */
+ inb(dev->iobase + DT2814_DATA);
+ inb(dev->iobase + DT2814_DATA);
+ }
+ return 0;
+}
+
static int dt2814_ai_eoc(struct comedi_device *dev,
struct comedi_subdevice *s,
struct comedi_insn *insn,
@@ -73,6 +110,7 @@ static int dt2814_ai_insn_read(struct comedi_device *dev,
int chan;
int ret;
+ dt2814_ai_clear(dev); /* clear stale data or error */
for (n = 0; n < insn->n; n++) {
chan = CR_CHAN(insn->chanspec);
@@ -174,6 +212,7 @@ static int dt2814_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
int chan;
int trigvar;
+ dt2814_ai_clear(dev); /* clear stale data or error */
trigvar = dt2814_ns_to_timer(&cmd->scan_begin_arg, cmd->flags);
chan = CR_CHAN(cmd->chanlist[0]);
--
2.30.0
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