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Joshua Oreman: 802.11 wireless development

Journal Week 12

I can hardly believe there's only a week left of SoC. It's been a wonderful experience working with such talented developers, and I hope my coursework in the fall will leave me enough time to continue contributing :-)

Also, I believe this IRC message needs to find a permanent record here:

10:45 <     mcb30> At the point you're talking about, the system is not fully initialised.  On many systems, the memory map
                   is not yet valid.  If running normal BIOS-level code is marked with "Here be dragons", running during POST
                   is marked with "Here be huge, ugly, vindictive, sociopathic dragons with a mean sense of humour"

Well put indeed.

Monday, 10 August

Not too much gPXE work today. I pushed a cleaned-up version of the large-ROM fix from my ath5k branch to staging as bigrom-oremanj (following the new staging tree protocol). A suggestion by Michael for making some of the condition checks for overflow more intuitive revealed the rather surprising fact that bit-shifting in C by more places than the size of the variable is undefined; on gcc-x86, 1ul « var when var is 32 will be not zero but one! This led to a small-scale audit of variable-amount bitshifts in the gPXE source, but I didn't find any code that would cause problems with this undefined behavior.

I received a new e1000 card, and was able to use it to restore the flash on the old one following a procedure that I've outlined on the ROM burning page. The issue was indeed one of option ROM overflow; gPXE loads to segment CC00, meaning it has exactly 80kB of ROM space on my test system. The ROM that had caused trouble was about 90kB.

I found a regression in the 802.11 code caused by recent changes to process_add() to ensure the same process is not added twice. The changes assume that all callers use process_init_stopped() to initialize all fields of the process structure, instead of setting just step and refcnt manually (which has worked fine in the past). The 802.11 code used the later method, and now does not start the association process at all. I pushed a two-line fix to staging as wiprocfix, and it probably will be merged tomorrow.

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