Thursday, August 11, 2005

Tuning the Shuttle BIOS

In an effort to squeeze a little more out of the my shuttle hardware (without increasing the heat output), I dived into the BIOS again.

This time, I was looking at memory issues. I was hoping to speed up memory access a little and find out why my 512Mb memory stick was only delivering 480Mb of usable RAM.

The size issue was due to the onboard ATI graphics stealing system RAM for it's framebuffer. The default setting is 32Mb and the minimum is 8Mb. I'm not using the onboard graphics for anything other than a virtual console which only needs a few kb of RAM. Reducing the 'UMI framebuffer size' (SP?) to 8Mb changed my usable memory from 479728k to 504176k. Useful.

With the speed issue, I tried playing with RAM timings and managed to reduce the latencies from 3-3-4-8 to 3-3-3-7. Anything less would cause a failure during extended testing with memtest86 or caused the shuttle to fail completely, requiring a BIOS reset.

While I was in the BIOS, I also tried lowering the CPU core voltage again. The default for my Celeron D is ~1.32v. I tested 1.2v and 1.1875v, both of which worked reliably under extended stress testing. I've left it at 1.1875v and I'll monitor the effect it has on heat output and assess long-term stability...

One last thing - ever since I've had it, my shuttle has exhibited a boot problem - it often fails to boot from cold, requiring perhaps one or two resets to get going. I think I might know why... While I was playing around, I noticed on 2 occassions that the BIOS had auto-detected the wrong FSB speed (166MHz instead of 133MHz) and was reporting my CPU as 3.15GHz w/ 664MHz internal FSB rather than 2.53GHz w/ 533MHz. That degree of inadvertent overclocking, without the corresponding voltage increase and cooling management is not going to work! I've now hardcoded the BIOS settings for FSB and memory speed to 133MHz and DDR-400 respectively.


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