[LinuxBIOS] Fun easy question. 512Kb or 256Kb

Richard Smith smithbone at gmail.com
Tue Feb 7 15:11:44 CET 2006

> Is there any thing from the Linuxbios side of the world, besides the
> size config?

Are you sure that your board has >=A18 routed to the chip for >=512k?
If not then those address lines might be no connects and they will
float.  Meaning that they can change on a whim.  If A18 changes you
will switch from 0-256k area to the 256k-512k and unless you have
duplicated the code into the area of the part things will go south.

> Does Linuxbios load the whole chip into ram(so 256k or 512k), or just
> it's self on startup?

It only copies what it thinks it needs.

> What controls that? Can I set/change the access speed to my "bios chip"?


> I have a few boards that had Eon chips(120ns), I have replaced them with
> SST's(45ns), they work fine.  Are they running faster?


This completely depends on the chipset and where your part is located.
 If you part is fetched via ISA cycles then there's not a lot you can
do.  Some chipsets will let you vary some ISA settings and perhaps the
number of wait states in the ISA cycle but normally that just lets you
slow down and not go faster.

If you can change the ISA clock then it _will_ go faster.  The ISA
clock probably comes from a source thats not variable or it may affect
other things in the system.  You will have to look at the chipset
docs.  I remember back in the good old AT "turbo" days that in turbo
mode the ISA clock was sometimes increased.  The coming of the vesa
local bus and then the PCI bus took care of that though.

If you bios is on the LPC bus then there might be some more
flexability.  I've not used the LPC bus much so I can't comment.

The same rules will mostly apply.  There will be a clock that drives
the bus.  Increase the clock you increase the bus speed.  If there is
a wait state > 0 setting it to 0 should increase the speed as well.

Expect to hang your system a lot while playing with this.

> On this current project all I care about is boot time and ever 0.10
> seconds I can save, counts.

I suspect that you have more success on speedups by tweaking the
linuxbios/linux kernel startup code than by trying to play with the
bios access times.

Sending a byte out the serial port at 115200 is approx 80 times slower
than a ISA bios fetch.  So you will have the most dramatic speed up by
nuking anything that writes to the serial port.

Richard A. Smith

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