On Mon, Oct 27, 2008 at 11:57:05AM -0400, John Baldwin wrote: > On Saturday 25 October 2008 04:09:45 am Jeremy Chadwick wrote: > > Just for posterity: the USB Legacy Support BIOS option does not affect > > natively-connected PS/2 keyboards; you can leave the option enabled even > > in the scenario where you have a USB keyboard *and* a PS/2 keyboard > > plugged in; one will not "trump" the other. Instead, you should have > > two keyboards which function in OSes/environments which lack a USB > > stack. (That is, until something resets/reassigns the BIOS-controlled > > interrupt, which will then break USB->PS/2 emulation; the native PS/2 > > keyboard should not be affected by this) > > This last statement is not quite true (at least not always true). For many > systems, the way the PS/2 emulation works is that accesses to the backing I/O > ports (0x60 and 0x64) case a trap into SMM and the SMI handler in the BIOS > then talks to the USB controller and keyboard and updates the register values > to simulate the I/O port accesses. This is disabled by having the USB host > controller driver frob flags in controller registers to disable the SMI > traps.
Thanks for cluing me in, John. I'm used to legacy device emulation being done purely from an interrupt handler point of view (BIOS mapping code to a specific interrupt), and wasn't even aware of SMM/SMI. -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB | _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[EMAIL PROTECTED]"
