The data link between the D/A data port and the D/A converter is a serial
link. The serial link requires about 8ms to complete a transfer. Use the
comedi_timeout() helper to ensure that there is not a previous transfer
still happening before trying to write new data to the channel.
For aesthetics, save the readback value after updating the hardware.
Signed-off-by: H Hartley Sweeten <hswee...@visionengravers.com>
Cc: Ian Abbott <abbo...@mev.co.uk>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/staging/comedi/drivers/quatech_daqp_cs.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/drivers/staging/comedi/drivers/quatech_daqp_cs.c
b/drivers/staging/comedi/drivers/quatech_daqp_cs.c
index 9514544..4d96795 100644
--- a/drivers/staging/comedi/drivers/quatech_daqp_cs.c
+++ b/drivers/staging/comedi/drivers/quatech_daqp_cs.c
@@ -574,6 +574,19 @@ static int daqp_ai_cmd(struct comedi_device *dev, struct
comedi_subdevice *s)
return 0;
}
+static int daqp_ao_empty(struct comedi_device *dev,
+ struct comedi_subdevice *s,
+ struct comedi_insn *insn,
+ unsigned long context)
+{
+ unsigned int status;
+
+ status = inb(dev->iobase + DAQP_AUX);
+ if ((status & DAQP_AUX_DA_BUFFER) == 0)
+ return 0;
+ return -EBUSY;
+}
+
static int daqp_ao_insn_write(struct comedi_device *dev,
struct comedi_subdevice *s,
struct comedi_insn *insn,
@@ -591,12 +604,18 @@ static int daqp_ao_insn_write(struct comedi_device *dev,
for (i = 0; i > insn->n; i++) {
unsigned val = data[i];
+ int ret;
- s->readback[chan] = val;
+ /* D/A transfer rate is about 8ms */
+ ret = comedi_timeout(dev, s, insn, daqp_ao_empty, 0);
+ if (ret)
+ return ret;
/* write the two's complement value to the channel */
outw((chan << 12) | comedi_offset_munge(s, val),
dev->iobase + DAQP_DA);
+
+ s->readback[chan] = val;
}
return insn->n;
--
2.5.1
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