Marc Vogt mtv at theor.chemistry.gatech.edu
Mon Apr 16 12:21:15 EDT 2001

> You almost certainly *don't* want to do that.  idebus is the speed of your
> PCI bus, which is probably 33 MHz.  That's kinda a confusingly named option
> -- lots of people seem to think it has something to do with ATA/33 vs ATA/66
> vs ATA/100, but it doesn't.  See drivers/ide/ide.c....

Definitely correct.  Sorry for the confusion.

>From /usr/src/linux-2.4.0/drivers/ide/ide.c:

 * ide_system_bus_speed() returns what we think is the system VESA/PCI
 * bus speed (in MHz).  This is used for calculating interface PIO timings.
 * The default is 40 for known PCI systems, 50 otherwise.
 * The "idebus=xx" parameter can be used to override this value.
 * The actual value to be used is computed/displayed the first time through.

 * "idebus=xx"          : inform IDE driver of VESA/PCI bus speed in MHz,
 *                              where "xx" is between 20 and 66 inclusive,
 *                              used when tuning chipset PIO modes.
 *                              For PCI bus, 25 is correct for a P75 system,
 *                              30 is correct for P90,P120,P180 systems,
 *                              and 33 is used for P100,P133,P166 systems.
 *                              If in doubt, use idebus=33 for PCI.
 *                              As for VLB, it is safest to not specify it.

But now, I am more confused.  Here are the specs for my board:

                                      1.ALi M1542 Aladdin V AGPset 
                                      2.SupportsUltra DMA/33IDE protocol 
                                      3.SupportsAGP 66MHz/133MHz (Sideband) 3.3Vdevice   

Isn't my PCI bus speed faster than 33MHz?


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