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MIPS: fix ROM exception vectors

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When booting from ROM, early exceptions can't be handled
properly. Instead of busy-looping give the developer the
possibilty to examine the situation. Invoke an UHI
exception operation which can be read as unhandled exception
by a hardware debugger if one is attached. If the debugger
doesn't support UHI, the exception is read as unexpected
breakpoint.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
This commit is contained in:
Daniel Schwierzeck 2016-02-07 19:39:58 +01:00
parent af3971f81a
commit 345490fcd6
1 changed files with 19 additions and 10 deletions
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29
arch/mips/cpu/start.S
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@ -52,6 +52,14 @@
.set noreorder .set noreorder
.macro uhi_mips_exception
move k0, t9 # preserve t9 in k0
move k1, a0 # preserve a0 in k1
li t9, 15 # UHI exception operation
li a0, 0 # Use hard register context
sdbbp 1 # Invoke UHI operation
.endm
ENTRY(_start) ENTRY(_start)
/* U-Boot entry point */ /* U-Boot entry point */
b reset b reset
@ -79,30 +87,30 @@ ENTRY(_start)
#endif #endif
#if defined(CONFIG_ROM_EXCEPTION_VECTORS) #if defined(CONFIG_ROM_EXCEPTION_VECTORS)
/*
* Exception vector entry points. When running from ROM, an exception
* cannot be handled. Halt execution and transfer control to debugger,
* if one is attached.
*/
.org 0x200 .org 0x200
/* TLB refill, 32 bit task */ /* TLB refill, 32 bit task */
1: b 1b uhi_mips_exception
nop
.org 0x280 .org 0x280
/* XTLB refill, 64 bit task */ /* XTLB refill, 64 bit task */
1: b 1b uhi_mips_exception
nop
.org 0x300 .org 0x300
/* Cache error exception */ /* Cache error exception */
1: b 1b uhi_mips_exception
nop
.org 0x380 .org 0x380
/* General exception */ /* General exception */
1: b 1b uhi_mips_exception
nop
.org 0x400 .org 0x400
/* Catch interrupt exceptions */ /* Catch interrupt exceptions */
1: b 1b uhi_mips_exception
nop
.org 0x480 .org 0x480
/* EJTAG debug exception */ /* EJTAG debug exception */
@ -222,6 +230,7 @@ reset:
move a0, zero # a0 <-- boot_flags = 0 move a0, zero # a0 <-- boot_flags = 0
PTR_LA t9, board_init_f PTR_LA t9, board_init_f
jr t9 jr t9
move ra, zero move ra, zero