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 <piel@xxxxxxxxxx> Fixes: 080e6795cba3 ("staging: comedi: ni_mio_common: Cleans up/clarifies ni_ao_cmd") Cc: Éric Piel <piel@xxxxxxxxxx> Cc: Spencer E. Olson <olsonse@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.7+ Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx> --- 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