Tuesday, May 1, 2012

USB composite device vs Gigabyte motherboards keyboard power-up

The two desktop in my home office feature recent Gigabyte motherboards, specifically models GA-990FXA-UD3 rev 1.1 and GA-890GPA-UD3H rev 2.1 .

One notable "feature" of these boards is that they only have a single PS/2 port for keyboard or mouse, but not both. This is a stupid design. If you use PS/2, you normally want to use it for both keyboard and mouse.

The omission of the second PS/2 port has forced me to purchase adapters to convert the PS/2 mouse signal to USB, more specifically the PS/2 mouse signal from my Iogear GCS84B KVM switch.

Simple passive adapters did not work. There was no mouse signal on the computer. I had to purchase smart active adapters. I literally tried 10 different models at Fry's Electronics and Micro Center before I found that was compatible with the mouse signal from the KVM switch, a noname one when I got the GA-890GPA-UD3H motherboard a year ago, and a Belkin model when I got the GA-990FXA-UD3 motherboard more recently.

These smart adapters actually take a pair of PS/2 signals for both keyboard and mouse, and turn it into a single USB signal. The computer sees it as a USB composite device.

I figured I would try to use it as designed, and connect both the keyboard and mouse to the adapter.

I immediately noticed a problem : I could no longer power the machine through the keyboard.

The BIOS on the motherboard normally allows you to power the system through the keyboard or mouse. You can select any key, or a password, or mouse motion or click. I choose a simple 1-character password option.

The feature just does not work when using the PS/2 to USB adapter . I tried all the possible options with mouse and keyboard. I set all the wake-up options to "Enabled" in the power management menu. But nothing worked, except pressing the power button on the front. This is OK for one of my systems that is close to my chair, but not OK for the other one.

This is a bit puzzling, because the BIOS otherwise supports the keyboard on this adapter just fine for purposes of entering into the BIOS setup menu.

I switched the keyboard connections back to the PS/2 port on both motherboards, leaving only the PS/2 mouse on the adapter, and powering up the machine through the keyboard worked fine again.

The lesson here is that 15-year old USB technology still has not caught up to good old PS/2. It could be argued that this is a problem with the motherboard implementation of USB power-on. But there are likely many other motherboards with the same problem.

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