As reported by Éric Piel on the Comedi mailing list (see
<https://groups.google.com/forum/#!topic/comedi_list/ueZiR7vTLOU/discussion>),
the analog output asynchronous commands are running too fast with a
period 50 ns shorter than it should be. This affects all boards with AO
command support that are supported by the "ni_pcimio", "ni_atmio", and
"ni_mio_cs" drivers.
This is a regression bug introduced by commit 080e6795cba3 ("staging:
comedi: ni_mio_common: Cleans up/clarifies ni_ao_cmd"), specifically,
this line in `ni_ao_cmd_set_update()`:
/* following line: N-1 per STC */
ni_stc_writel(dev, trigvar - 1, NISTC_AO_UI_LOADA_REG);
The `trigvar` variable value comes from a call to `ni_ns_to_timer()`
which converts a timer period in nanoseconds to a hardware divisor
value. The function already reduces the divisor by 1 as required by the
hardware, so the above line should not reduce it further by 1. Fix it
by replacing `trigvar` by `trigvar - 1` in the above line, and remove
the misleading comment.
Reported-by: Éric Piel <p...@delmic.com>
Fixes: 080e6795cba3 ("staging: comedi: ni_mio_common: Cleans up/clarifies
ni_ao_cmd")
Cc: Éric Piel <p...@delmic.com>
Cc: Spencer E. Olson <olso...@umich.edu>
Cc: <sta...@vger.kernel.org> # 4.7+
Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
---
The bug is also in 4.6.x, but this patch does not apply to it cleanly.
---
drivers/staging/comedi/drivers/ni_mio_common.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c
b/drivers/staging/comedi/drivers/ni_mio_common.c
index b2e382888981..2f7bfc1c59e5 100644
--- a/drivers/staging/comedi/drivers/ni_mio_common.c
+++ b/drivers/staging/comedi/drivers/ni_mio_common.c
@@ -3116,8 +3116,7 @@ static void ni_ao_cmd_set_update(struct comedi_device
*dev,
/* following line: 2-1 per STC */
ni_stc_writel(dev, 1, NISTC_AO_UI_LOADA_REG);
ni_stc_writew(dev, NISTC_AO_CMD1_UI_LOAD, NISTC_AO_CMD1_REG);
- /* following line: N-1 per STC */
- ni_stc_writel(dev, trigvar - 1, NISTC_AO_UI_LOADA_REG);
+ ni_stc_writel(dev, trigvar, NISTC_AO_UI_LOADA_REG);
} else { /* TRIG_EXT */
/* FIXME: assert scan_begin_arg != 0, ret failure otherwise */
devpriv->ao_cmd2 |= NISTC_AO_CMD2_BC_GATE_ENA;
--
2.11.0
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