I got a patch from the original author, Fred Brooks, to add a small
settling delay after setting the AI channel multiplexor. The lack of
delay resulted in unstable or scrambled data on faster processors.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
Reported-by: Fred Brooks <nsaspook@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 3.7.x - 3.15.x
---
drivers/staging/comedi/drivers/ni_daq_700.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/staging/comedi/drivers/ni_daq_700.c b/drivers/staging/comedi/drivers/ni_daq_700.c
index 171a71d..728bf7f 100644
--- a/drivers/staging/comedi/drivers/ni_daq_700.c
+++ b/drivers/staging/comedi/drivers/ni_daq_700.c
@@ -139,6 +139,8 @@ static int daq700_ai_rinsn(struct comedi_device *dev,
/* write channel to multiplexer */
/* set mask scan bit high to disable scanning */
outb(chan | 0x80, dev->iobase + CMD_R1);
+ /* mux needs 2us to really settle [Fred Brooks]. */
+ udelay(2);
/* convert n samples */
for (n = 0; n < insn->n; n++) {
--
1.9.2
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