Analog Triggering and Interrupt generation on the PCIe-6320 under Linux

Question

We would like to use the analog triggering functions of the PCIe-6320 under Linux to time tag external events.
I have no experience with the MH DDK but have been told this is what we would need to implement the functions we want. We plan on using Fedora Linux and we are targetting kernel 2.6.31 with the PREEMPT_RT patch applied. We may consider slightly more recent kernel versions. The PREEMPT_RT patch is used to greatly improve determinism in the system and get real-time responses to some external events.
Here is what we wish to do in more details:
We wish to route at least two analog inputs to the comparator, then route the output of the comparator to a digital input which in turn would create a PCIe interrupt. The interrupt software handler would than time tag that event for our application purposes. We need the comparator threshold to be software programmable in level and slope. We are also interested in using the Watchdog Timer feature of the board.
Our application is written in C/C++.
Would the above be feasible? Please provide comments and instructions how we should address our requirement.
Thanks!

Answer 1

Patof wrote:
I am not familiar with the MHDDK. I would like to have an idea of the effort required to implement the functions I have described using MHDDK on Linux. Like I mentionned, we plan on using Linux kernel 2.6.31 with the PREEMPT_RT patch. Could you provide comments on that matter? I need to evaluate the amount of time I will need to spend to deploy and use MHDDK for the PCIe-6320.
There are two factors to consider when writing a driver for your specific application:
Using the deterministic kernel API calls
Writing to the device registers to
Control the watchdog timer
Configure the analog comparator
Manage the analog subsystem state as trigger events occur
Handle device interrupts
The MHDDK for X Series offers the following behavior out-of-the-tarball:
A Linux kernel module using the standanrd kernel and PCI subsystem calls
Mapping device registers to user-mode for access
Demonstrating/documenting how to
Control the watchdog timer (dioex6.cpp)
Manage the analog subsystem state as trigger events occur (aiex2.cpp, aiex4.cpp)
Handle device interrupts (reference manual only)
There are two notably missing pieces and one item to consider:
Missing: deterministic kernel API calls. If you decide to use the nirlpk module, you would need to change it from the standard interfaces to the deterministic variants.
Missing: configuring the analog comparator. You will need to implement this with additional insight from this discussion board.
Consider: if your application requires device access from kernel-mode only, you would not be able to use the MHDDK's C++ classes that perform device programming but would need to implement register programming in C.
To estimate the time for these three, here are my recommendations:
Review the nirlpk.c source file to understand how device access and DMA buffers are implemented and mapped to the user-mode application.
Beware that operation-specific programming help (as you would need for analog triggering) typically requires two weeks for a complete response.
Review the ChipObjects in the MHDDK distribution to understand how register addresses, widths, and bit fields affect device programming.
Joe Friedchicken
NI VirtualBench Application Software
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