Subject: 710/720 differences

From: Dan Conti <[email-masked]>
Date: Thu, 19 Aug 1999 17:25:29 -0700 (PDT)

Hello everyone,

I am working on porting linux to an arm720 chip that i am currently
working with, and i've run into a bit of a hitch. I can build kernel
images that work with (relatively) minimal problems (such as paging
issues) on an arm710 chip I am working with, but i'm having difficulty
with the 720 version. I added a mask in the ProcTypes list in head-armv.S
for the 720 processor id, and created a new set of processor functions
(arm720_processor_functions) to properly flush the TLB and the cache,
since the coprocessor registers are slightly different on the 720, but i'm
not really sure what else needs to be modified. Most of my kernel appears
to be working, I get up to a point where the kernel attempts to open
/dev/console (in init/main.c), at which point it falls flat on its face
with a file not found. My setup is a bit wierd, the 720 i am working with
is completely diskless, so the root file system is in a ramdisk, but i
know this works (or, at least, it works on the 710 system i have). The
root file system properly mounts.

I have traced execution all over trying to track down exactly what goes
on, but i can't exactly determine what difference between the two chips
would allow one kernel/ramdisk image to work fully on the 710 but cause it
to fail so late in the game on the 720. So right now i'm trying to gather
information of any sort, if anyone has experience with 710 and 720 chips
and provide any information or resources on casual or glaring distinctions
between the two, i'd be really appreciative. I'm sorry if i'm a little
vague on detail, i'm hesitant to release information regarding the
specifics of what i'm working with.

Any help would be greatly appreciated...Thanks in advance,
-Dan

unsubscribe: body of `unsubscribe linux-arm' to [email-masked]

---

From: "Adam 'WeirdArms' Wiggins" <[email-masked]>
Date: Fri, 20 Aug 1999 22:22:10 +1000 (EST)

I think the only real difference between the MMU's of the 710 and
the 720 is that teh 720 has some of the features of the SA-1100. That is
the ability to relocate teh exception vector to 0xFFFF0000 and the PID
(Process ID) register to relocated the first 32MB of the virrtual address
space to another 32MB region. These are listed as so called WinCE
enhancements and only work when the WinCE pin is active on the chip.
Refere to the ARM manuals on the chips for more detial.

	Cheers Adam

---

From: Philip Blundell <[email-masked]>
Date: Sat, 21 Aug 1999 22:26:41 +0100

>with a file not found. My setup is a bit wierd, the 720 i am working with

Can you post the exact messages you get at bootup?  If /dev/console can't be 
opened did you check that it really does point to a valid console device?

I can't think of anything about the 720 that would cause this off the top of 
my head.  Just adding support in the places you did should be enough.  It has 
some features that the 710 lacks but these should be benign if you just ignore 
them.

My suspicion is that your problem lies elsewhere than with the CPU.

p.