Autobahn Device Driver for Linux 2.6

The NIST PCI card driver has recently been ported to the 2.6 linux kernel. This page documents the changes and bugs fixed.

One major change is the correction of the ab_poll() function, normally entered when the application calls the system poll(2) or select(3). In 2.4, the application sets up for asynchronous I/O; then synchronously waits by calling poll(). This is no longer required, nor advised. If the application wants to wait synchronously it should just call poll(). ()

Porting Changes

The ab_poll() function:

There were a number of bugs in this function.

The ab_poll() function accessed the hardware's current state to determine if an interrupt had occurred. This is poor practice and has been removed.
The function did not use any type of wait queue mechanism. A wait queue has been added.
The function used a copy of a data structure rather than a pointer to the main object. This is an error.

The ab_mmap() function:

Changed memory mapping to use 2.6 'pfn' type API to manipulate memory page tables.
Updated to use 2.6 release of bigphysmem kernel patch.

The init_module() function:

Updated driver registration and pci detection calls to current kernel API.
Added initialization of wait queues mentioned above.

Open Issues:

For a reason not yet understood, card interrupts are not detected when the BIOS allows the AIOPIC to operate in 'advanced' mode, the old XT-PIC mode must be used.
The driver still has artifacts which confound things. Although it was originally written to support multiple cards, I don't think it is 100% there yet.
ab_poll() clears a flag which indicates an interrupt has occurred, assuming the application has been notified. I suppose this is OK, but it does prevent multiple applications from both waiting on the same card.

Other Improvements

Addition of a timeval/timestamp to each buffer. Not yet implemented. ( -- as of Jan 2008, Ray has added this to our version of the driver)
Addition of an entry in /proc of 'aa_info'. This outputs a hex dump of a portion of ab0's buffer, along with other debug information. (Added in 2.4 version as well.)

-- JoeBrandt - 23 Aug 2007

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