P3 underclock/undervolt (homemade router question)

star882 · Post by **star882** » Fri Jan 26, 2007 1:27 pm

If I underclock a 733MHz P3 (Coppermine, 1.65v default) to 550MHz or 366MHz, about how much can I reduce the voltage and still get reliable operation?
Note that the main objective of reducing heat is to make it easier to design and reduce the size of power supply circuits. Low noise is an objective but not the main one. The case is small (just enough to fit the motherboard, NICs, custom DC/DC converters, and 2.5" HDD), so a large heatsink is not a good option. I could use Freon-based heatsinks but I think they're pretty overkill for a router.

Bobfantastic · Post by **Bobfantastic** » Fri Jan 26, 2007 1:55 pm

I think the law of diminishing returns comes into play here, in that there's no straight-line relationship between voltage and speed. Also, no matter how low you set the clock speed, it will refuse to run after a certain point as you lower the voltage.

You'll need to go by trial and error, I'm afraid. Being an older process, the chances are that there was more sample-variability. You should manage about 1v, more or less, but again that could well be nonsense. By the by, I'd be interested to find out how well the system works under heavy loads- seriously under-clocking a dated processor, then loading it up with what I presume are Gig-E cards? Seems to me that you'd be better more or less keeping the stock speed, and seeing how low you can go. Crippling the processor to save 0.01v won't be worth it if the system takes three or four times as long to complete the same task.

Incidentally-"overkill for a router"? Building your own is overkill for a router!

Oh, and one more thing... Welcome to SPCR!

star882 · Post by **star882** » Fri Jan 26, 2007 2:25 pm

Bobfantastic wrote:I think the law of diminishing returns comes into play here, in that there's no straight-line relationship between voltage and speed. Also, no matter how low you set the clock speed, it will refuse to run after a certain point as you lower the voltage.

You'll need to go by trial and error, I'm afraid. Being an older process, the chances are that there was more sample-variability. You should manage about 1v, more or less, but again that could well be nonsense. By the by, I'd be interested to find out how well the system works under heavy loads- seriously under-clocking a dated processor, then loading it up with what I presume are Gig-E cards? Seems to me that you'd be better more or less keeping the stock speed, and seeing how low you can go. Crippling the processor to save 0.01v won't be worth it if the system takes three or four times as long to complete the same task.

Incidentally-"overkill for a router"? Building your own is overkill for a router!

Oh, and one more thing... Welcome to SPCR!

No, it's plain 10/100. And even an underclocked P3 will have more than enough capacity. I have an old 200MHz Pentium Pro operating at about 30% routing under heavy load. However, that machine is starting to break down so I'm building a new one.
In any case, it will be far more powerful than a common DSL router. And that's the reason why I built a router - the 8MB in a typical router just can't take the load! (And no, I'm not willing to spend more than $100 on a router - I've been disappointed by an $80 router so I'd rather recycle some old parts and build my own.)

star882 · Post by **star882** » Sat Jan 27, 2007 5:48 pm

I set the voltage to 1.3v (as low as it will go without replacing the voltage reference) and set the clock to 550MHz. Using a Pentium 1 heatsink, it remained cool with just 5v on the fan. And at 5v, the fan was more or less silent. It passes memtest86 and some CPU stress programs so I consider that part done. Now to design the custom power supply and install ClarkConnect Community Edition...

Cerberus · Post by **Cerberus** » Sat Jan 27, 2007 7:53 pm

I hope you start a thread in the General Gallery forum soon. I want to hear more about this project...

autoboy · Post by **autoboy** » Sat Jan 27, 2007 8:24 pm

My Netgear rangemax 240 was $40 because it was going out of stock at frys. It is one of the best routers available. It can handle 194 connections and 96mbit WAN speeds.

star882 · Post by **star882** » Sat Jan 27, 2007 9:23 pm

autoboy wrote:My Netgear rangemax 240 was $40 because it was going out of stock at frys. It is one of the best routers available. It can handle 194 connections and 96mbit WAN speeds.

I'm making a router that is more of a firewalled gateway (basically a DIY "Cisco"), not a WAP. I already have some nice wireless routers (which I'm working on to run custom software), two of which already have high gain antenna mods.
BTW, I have actually spent only a little above $2 on the homemade router - just above $1 each for the two NICs. So far, everything else is recycled. $40 is pretty good for a "pre-N" router, but I think I'll wait for the official N. By then, the pre-N units should be down to $10 during sales just like some G units have...

Oh, and as for that old Pentium Pro (might actually be a Pentium MMX - it's been so long that I don't remember what I put in it!), I plan to take it all apart once I finish building the new router, then repair it if it is just a simple problem (probably a blown cap - had one go in the first few days causing the connection uptime counter to glitch) and repackage the machine in a compact box as a monowall unit.

psiu · Post by **psiu** » Sun Jan 28, 2007 2:38 pm

Cool project--I actually have roughly the same thing running already.

P3-450
384 MB PC100 (I have nothing else to stick this PC100 ram in

)
2 SMC 10/100 NICs
256 MB CF card with CF=>IDE adapter

Runs BrazilFW nicely--firewall, router, VPN, and if I ever get around to it, a WAP gateway as well. Both the memory and CF card are way overkill. The P3 probably is as well--but it was free also. Even a Pentium is far and away more than enough, but the boards are all dying by now.

star882 · Post by **star882** » Sun Jan 28, 2007 8:26 pm

psiu wrote:Cool project--I actually have roughly the same thing running already.

P3-450
384 MB PC100 (I have nothing else to stick this PC100 ram in )
2 SMC 10/100 NICs
256 MB CF card with CF=>IDE adapter

Runs BrazilFW nicely--firewall, router, VPN, and if I ever get around to it, a WAP gateway as well. Both the memory and CF card are way overkill. The P3 probably is as well--but it was free also. Even a Pentium is far and away more than enough, but the boards are all dying by now.

What power supply are you using with it? Do you have any plans to make one from an old laptop power supply and some digital voltage regulators like I plan? (I'll also have to make it power the OLED backlight on the LCD I'm using. I might have to spread spectrum the switcher to keep it from squealing when in operation.)
BTW, I'll see if I can make the case for my router my CAD class project so I can laser cut the case to exactly the right size, along with the holes for the I/O ports, front panel LCD, and cooling vents. I'm not sure what materials the laser can work with but I do know it's too hot for anything plastic. If that plan doesn't work, either I'll find something to use as a case or turn it into a "maxi router" project that integrates lots of other network hardware.

psiu · Post by **psiu** » Mon Jan 29, 2007 2:59 am

Using some crappy power supply (300w raidmax? maybe) with it right now. Should do a fan swap, dremel out the grill, but I'm lazy. In an old case for now. It would be a good candidate for building a tiny case and using one of those picoPSU's for it like you're doing--but it works *shrugs*.

I use it in conjunction with a Motorola wireless router set to AP mode.

I have a free DLink router I picked up also...I should use that as target practice

psiu · Post by **psiu** » Mon Jan 29, 2007 12:15 pm

Actually the best solution I've seen is what my friend has running--a headless P3 laptop with a CF card as boot device for his router/firewall.