[U-Boot-Users] IVT on 405GP
wd at denx.de
Wed Apr 16 21:16:53 CEST 2003
in message <EGEGIJHKDKJGAJMGIDPNMEPACKAA.jwalden at digitalatlantic.com> you wrote:
> Just reading some uboot install stuff and it appear to say what I am
> doing is ok but it does not seem to do everything. It say that it copies
> itself to upper memory then it should copy 8k of vector stuff to zero. So
> it looks like somehow I am missing the vector copy code, or it is not
> Again it appears as though "trap init" initializes some vectors in the IVT,
> however it does not copy the code prologue and exception code.
> Can you see in the code where the contents of the first 8k of memory
> is copied?
I really don't understand what this discussion is all about.
Please look at the code yourself. It is not that complicated to
understand. See "cpu/ppc4xx/start.S":
1367 * Copy exception vector code to low memory
1369 * r3: dest_addr
1370 * r7: source address, r8: end address, r9: target address
1372 .globl trap_init
1374 lwz r7, GOT(_start)
1375 lwz r8, GOT(_end_of_vectors)
1377 rlwinm r9, r7, 0, 18, 31 /* _start & 0x3FFF */
1379 cmplw 0, r7, r8
1380 bgelr /* return if r7>=r8 - just in case */
1382 mflr r4 /* save link register */
1384 lwz r0, 0(r7)
1385 stw r0, 0(r9)
1386 addi r7, r7, 4
1387 addi r9, r9, 4
1388 cmplw 0, r7, r8
1389 bne 1b
Guess what this 1: ... "bne 1b" loop is doing?
The code is really simple, and I don't know why you are missing it
when reading the sources or when running under a debugger. And the
function name "trap_init()" is IMHO well chosen and descriptive
enough, too. And there is even a comment which explains what it does.
The only thing I can see that could go wrong here is that the
computation of the end address (r9 = _start & 0x3FFF) might fail if
you pass bogus values for _start to that code. Please note that the
code assumes that it has been started from the reset entry point, i.
e. _start is at a well known address, and "_start & 0x3FFF" is
equivalent to 0x100 ;-) But then, this should be trivial to check,
and I assume you already checked it under a debugger, didn't you?
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
If it has syntax, it isn't user friendly.
More information about the U-Boot