hlide
Joined: 10 Sep 2006
Posts: 750
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 Posted: Thu Jan 11, 2007 6:30 am Post subject: ME cpu has two unknown instructions |
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when looking at mips-opc.c i was intrigued to see them :
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{ "ldl", "t,o(b)", 0x68000000, 0xfc000000, LDD|WR_t|RD_b, 0, I3|AL },
{ "sdl", "t,o(b)", 0xb0000000, 0xfc000000, SM|RD_t|RD_b, 0, I3|AL },
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are "defined" for allegrex where as :
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{ "ldr", "t,o(b)", 0x6c000000, 0xfc000000, LDD|WR_t|RD_b, 0, I3 },
{ "sdr", "t,o(b)", 0xb4000000, 0xfc000000, SM|RD_t|RD_b, 0, I3 },
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are not "defined" for allegrex.
PSP is not a MIPS64, so PSP shouldn't know those both instructions which are for unaligned doubleword load/store.
There is only one possibilty : ldl/sdl are special instructions which have a different goal.
Indeed they seem to be used a lot on ME processor, just one example :
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sub0(arg1, arg2, arg3):
addiu $sp, $sp, -0x10
sw $ra, 0xC($sp)
sw $s2, 0x8($sp)
move $s2, $a2
sw $s1, 0x4($sp)
move $s1, $a1
sw $s0, 0x0($sp)
move $s0, $a0
move $a0, $zr # int timeout = 0;
0: ldl $a1, 0x200($a3) # loop: ready = vme_bus[0x200]; (?)
addiu $a0, $a0, 0x1 # timeout++;
andi $v0, $a1, 0x1
bnez $v0, 1f # if (ready & 1) goto goon;
slti $v1, $a0, 0x1000
bnez $v1, 0b # if (timeout < 0x1000) goto loop;
nop
jal sub1 # sub1(0xD); // reset ?
li $a0, 0xD
1: sdl $s0, 0x200($a3) # goon: vme_bus[0x200] = arg1; (?)
sdl $s1, 0x201($a3) # vme_bus[0x201] = arg2; (?)
sdl $s2, 0x202($a3) # vme_bus[0x202] = arg3; (?)
move $v0, $zr
sdl $v0, 0x203($a3) # vme_bus[0x203] = 0; (?)
lw $ra, 0xC($sp)
lw $s2, 0x8($sp)
lw $s1, 0x4($sp)
lw $s0, 0x0($sp)
jr $ra
addiu $sp, $sp, 0x10
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two remarks :
- $a3 is a dummy register so i suspect those instruction not to have a base register (their base opcodes seem to be more like 0x68E00000 and 0xB0E00000 than 0x68000000 and 0xB0000000)
- the offset should probably be an immediate (the biggest value I found out is 0x58F, which an immediate value encoded less than 12 bits).
so i suspect those both instructions to be something like :
ldl $v0, 0x200($a3) ==> mfvme $v0, $200 <=> $v0 = vme_bus[0x200]
sdl $v0, 0x200($a3) ==> mtvme $v0, $200 <=> vme_bus[0x200] = $v0
is it for VME ? is it for AVC decoder ? dunno. |
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