On Tuesday 08 April 2008, Joakim Tjernlund wrote:
On 4xx execution always starts at 0xfffffffc (last lword in 32bit address space). This location holds a jump to _start for 405 PPC's and to _start_440 for 440 PPC's. 440 PPC's need some extended initialization (TLB setup etc) and later jump to the 4xx common _start.
OK, then it is like I suspected. What if you rename _start to _common_start. Make _start equal _common_start for 405 and rename _start_440 to _start, i.e make sure that _start is defined where you start executing after the jump.
As I mentioned earlier, _start_440 is mapped to 0xfffff000 via the linker script since the jump from 0xfffffffc can't be too long (because of the 4k shadow TLB entry). So renaming _start_440 to _start won't help here. It can be done, but frankly I don't have the time for it currently.
I'm an linker script dyslexic. So no idea if we can handle this solely in the linker script or if we need a new common symbol in the PPC start.S's.
Both ways should be doable I think. A linker script would probably look something like(pseudo diff below): .text : {
- _monitor_base = . ;
- PROVIDE (_monitor_base = .); cpu/mpc83xx/start.o (.text)
And then add a GOT_ENTRY(_monitor_base) in start.S
The disadvantage I see is that I need to change the linker scripts for all boards for such a solution. Doesn't sound like fun.
So for now, I would really like to see the old version with the ugly CFG_MONITOR_BASE back so that 4xx board can be used again.
Best regards, Stefan
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