ASRock 939Dual-SATA2 Command Rate Problem

The hardware in question is the ASRock 939Dual-SATA2 motherboard as well as 2x 512MB Kingston ValueRAM. Nothing fancy, but I’d at least expect stability.

I didn’t run into this problem myself; it happened on the family computer. Main symptom – random reboots by the computer. They curiously happened only in Civilization IV and some random websites with Flash objects. I ran system stability tests like Prime/Orthos, tested the memory with Memtest86 and looped some graphics benchmarks. Nothing was out of the ordinary. There were no reboots or hard locks that would indicate a hardware problem.

But the problems were definitely there and they weren’t going away. I reformatted more than once and tried different video drivers with no luck. Even a cursory glance through the Google results for the problem recommended new PSUs or perhaps a busted processor. I in fact did try a different power supply; that didn’t help either. I thought perhaps it was the HDTV not playing well with the system, but hooking up a normal LCD monitor didn’t correct the problem.

I dug deeper and started finding people who had reboots on random webpages with Flash objects. Turns out this motherboard doesn’t like the 1T command rates too much. There were a few workarounds suggested, such as setting the burst length to a lower setting, but I decided to play it safe. After a quick reboot to the BIOS and setting the command rate down to 2T, everything’s fine and dandy. No more reboots! That 2-5% performance loss due to a lower command rate? Ah well, the folks will just have to live with that.


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