Hi Alexis,

  maybe it is more useful to mention what I actually want to achieve with DIO 
on my NI6259.  My DIO communication involves a series of interactions with 
another board to collect sensory data from a robot, and to send out commands to 
this board. For instance, to read one of the sensors, a sequence of DIO values 
need to be written to tell the board to send the data. I programmed this 
initially with synchronous instructions using a4l_sync_dio(), but this turns 
out to be too slow. Thus, the hope is to use commands, i.e., fill the FIFO with 
the sequence of values which I need to execute, and then use asynchronous DIO 
to obtain much higher speed of communicating the values in the FIFO.

   Thus, what I essentially try to do is to put about 10-20 scans in the FIFO, 
and then write the FIFO as fast as possible to my NI6259 DIO subdevice.

Would you have any ideas how to do this fast writing of the scans in the FIFO 
with the current analogy functionality?

Thanks a lot!


On Jul 12, 2010, at 22:51, Stefan Schaal wrote:

> Hi Alexis,
>  thanks a lot for the explanations. One item I am confused about is that you 
> write that TRIG_TIMER is not suitable for DIO, but in cmd_write.c in your 
> sample code, it is used for the analog write without problems. Wouldn't one 
> be able to just use the same clock source for DIO as in analogue I/O?
> Best wishes,
> -Stefan
> On Jul 12, 2010, at 15:29, Alexis Berlemont wrote:
>> Hi,
>> Stefan Schaal wrote:
>>> Hi Alexis,
>>> I guess I slowly understand that my clocking signal connected to
>>> scan_begin_arg has to come from an external DIO input, if
>>> scan_bigin_src = TRIG_EXT, and that the insn instruction is still
>>> needed to trigger the entire acquisition. 
>> Yes. The trigger instruction is needed so as to start the whole
>> acquisition (which is composed of many scans). A periodic external
>> signal is needed so as to trigger each scan.
>>> Alternatively, would it be possible to use the internal clocking signals 
>>> like 
>>> scan_bigin_src = TRIG_FOLLOW
>>> or 
>>> scan_bigin_src = TRIG_TIMER
>> I think you are right. If the sampling clock comes from another
>> subdevice, TRIG_EXT may not be the most appropriate constant. However,
>> the original comedi driver only expects TRIG_EXT even if... the
>> sampling signal is not external.
>> TRIG_TIMER does not seem suitable because it assumes an independant
>> sampling clock is available.  
>> And TRIG_FOLLOW may be the most appropriate one. We should modify the
>> driver so that TRIG_FOLLOW is used if the analog sampling clock is
>> chosen.
>>> if I try any of these sources, I get an error -22, and dmesg reports:
>>> [195882.321300] Analogy: a4l_check_cmddesc: scan_begin_src, trigger 
>>> unsupported
>> For me, the command interface is an empty shell because the various
>> parameters (start_src, scan_begin_src, ...) and the values (TRIG_*)
>> are imposed. And, on the other side, the driver is fully in charge of
>> the command structure as it is. So, the comedi command imposes a
>> communication method but does not ease the driver's task of managing
>> it (errors checking, translation, etc.)
>> And, in our case: DIO, we may conclude that this imposed API does not
>> fit well: in scan_begin_arg, we have to pass an index which is
>> supposed to correspond to some sampling clock (which is specific to a
>> board). Then, we use a generic interface with board-specific
>> arguments.
>> So, to sum up, I understand your point: the way we control the driver
>> may not always be the most appropriate one. But, we inherited from
>> comedi both the interface and the drivers. 
>> On my side, I am working on trying to implement (as a background task)
>> a generic interface a little bit more based on discovery (query /
>> enum) that would render the command interface obsolete. Unfortunately,
>> I have nothing interesting to show yet.
>>> Best wishes,
>>> -STefan
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