Hi,
I think you need to re-think your comedi stance. If you use the rtlinux api
to the comedi drivers there is not that much framework to deal with. The
rtlinux api to comedi is primarily an interface to the driver. There are
other simple drivers available for digital I/O and DACs but ADCs are
inherently more complex due to the fact that there are conversion times
involved before the data is available. This is where comedi steps in. The
api for comedi has a mechanism that has the card generate an interrupt when
the conversion is complete. The interrupt routine can then make a function
call and get the data. Due to timing issues for data availability I elected
to have this interrupt from the ADC card control the timing of the entire
real time task.
The initial call to setup the PCI card can look cumbersome at first but it
really is not that difficult once you understand the parameters. It really
would not matter which ADC card you are using most of the parameters would
have to be set up in the beginning before you could use it. Furthermore,
the setup routine is only run once when the module is installed. After that
the only comedi routine you call is the one to get the data.
I am currently using a National Instruments PCI-6033 but I have since found
that I can get the same card through Computerboards that has twice the
throughput at half the cost. It has way more channels that you need but I
thought I would be more specific in my discussion here.
If you really want a driver that is very specific to your task then you
might want to grab the register level code of the comedi drivers and modify
it to your specific needs. I was in the same frame of mind when I went
looking for hardware and I found that for PCI ADCs it was much easier to use
the rtlinux api to comedi and doing so did not have any impact on the
performance of the rtlinux task.
It is easier to look for linux drivers and then choose the card from these
candidates than to look at hardware and then try to find a driver.
I would send you a snippet of my code but I can't get at the machine today.
I am a lucky soul and get to go to the embedded linuxworld conference next
week in San Francisco, California so I won't be able to do it next week
either. If you remind me at the end of next week I think could do it then.
regards,
Rich
-----Original Message-----
From: Stephen D. Cohen [mailto:[EMAIL PROTECTED]]
Sent: Friday, August 24, 2001 5:51 AM
To: '[EMAIL PROTECTED]'
Subject: [rtl] Need Board Recommendations - ADC, Serial I/O
Gang,
I am working on a new application that requires joystick input from
a high quality joystick. This is done with an ADC card and some digital I/O
lines (for buttons). I am looking for a card that is easy to use that has
at least two channels of analog input of at least 12 bits each and at least
eight lines of digital I/O. Can anyone recommend any particular card for
this application? Any options that include source for an RTLinux driver are
greatly preferred. :-)
I am also looking for an eight-port serial board. Can anyone
recommend a board for use with either straight Linux or rt_comm or,
preferably, both? I would really like to find a board that uses the same
IRQ / port sharing / mapping scheme as the base four ports of the PC
architecture. That way it would be pretty simple to extend the rt_comm
stuff to handle the additional ports. If anyone has done anything like this
or can recommend a card, I would love to hear about it.
I can obviously find many references to boards from the likes of
Data Translations, Computerboards, etc. What I am looking for is
testimonials to ease of use or cards for which drivers are available. I
know about Comedi, but I am not really interested in having additional
framework - I just want something small and tight to read the channels and
buttons when I want the input.
Both of these cards need to be PCI cards for the standard IBM-PC
architecture.
Regards,
Steve Cohen
--------------------------
Stephen D. Cohen
Xybion Sensor Positioning Systems
11528 53rd Street North
Clearwater, FL 33760
Voice: (727) 299-0150
Fax: (727) 299-0804
[EMAIL PROTECTED]
www.xybion.com
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