Mit6.004-lab09-Emulating Instructions

一、 以软件形式添加LDB/STB

.include “beta.uasm”
.include “checkoff.uasm”

regs:
RESERVE(32) // Array used to store register contents

UI:
save_all_regs(regs)

LD(xp,-4,r0) // illegal instruction
extract_field(r0,31,26,r1) // extract opcode, bits 31:26
CMPEQC(r1,0x10,r2) // OPCODE=16?
BT(r2, LDB) // yes, handle the swapreg instruction.
CMPEQC(r1,0x11,r2) // OPCODE=17?
BT(r2, STB)

LD(r31,regs,r0) // Its something else. Restore regs
LD(r31,regs+4,r1) // we’ve used, and go to the system’s
LD(r31,regs+8,r2) // Illegal Instruction handler.
BR(_IllegalInstruction)

LDB:
extract_field(r0,20,16,r2) // extract ra field from trapped instruction
MULC(r2, 4, r2) // convert to byte offset into regs array
LD(r2, regs, r4) // r4 <- regs[ra]
extract_field(r0,25,21,r1) // extract rc field from trapped instruction
MULC(r1, 4, r1) // convert to byte offset into regs array
LD(r1, regs, r3) // r3 <- regs[rc]
SHLC(r0, 16, r2)
SRAC(r2, 16, r2)
ADD(r4, r2, r4)
LD(r4, 0, r5) // MDATA
extract_field(r4,1,0,r4) // EA1:0
CMPEQC(r4, 0, r8)
BT(r8, L0)
CMPEQC(r4, 1, r8)
BT(r8, L1)
CMPEQC(r4, 2, r8)
BT(r8, L2)
CMPEQC(r4, 3, r8)
BT(r8, L3)
L0:
extract_field(r5,7,0,r7)
BR(L4)
L1:
extract_field(r5,15,8,r7)
BR(L4)
L2:
extract_field(r5,23,16,r7)
BR(L4)
L3:
extract_field(r5,31,24,r7)
L4:
ANDC(r3, 0, r3)
OR(r3, r7, r3)
ST(r3, regs, r1)
restore_all_regs(regs)
JMP(xp)

STB:
extract_field(r0,20,16,r2) // extract ra field from trapped instruction
MULC(r2, 4, r2) // convert to byte offset into regs array
LD(r2, regs, r4) // r4 <- regs[ra]
extract_field(r0,25,21,r1) // extract rc field from trapped instruction
MULC(r1, 4, r1) // convert to byte offset into regs array
LD(r1, regs, r3) // r3 <- regs[rc]
SHLC(r0, 16, r2)
SRAC(r2, 16, r2)
ADD(r4, r2, r4) // EA
LD(r4, 0, r5) // MDATA
extract_field(r3, 7, 0, r3) // RC7-0
extract_field(r4, 1, 0, r9) // EA1:0
CMPEQC(r9, 0, r8)
BT(r8, A0)
CMPEQC(r9, 1, r8)
BT(r8, A1)
CMPEQC(r9, 2, r8)
BT(r8, A2)
CMPEQC(r9, 3, r8)
BT(r8, A3)
A0:
ORC(r9, 0xffff, r9)
ANDC(r9, 0xff00, r9)
BR(A4)
A1:
SHLC(r3, 8, r3)
ORC(r9, 0xffff, r9)
SHLC(r9, 16, r9)
ORC(r9, 0x00ff, r9)
BR(A4)
A2:
SHLC(r3, 16, r3)
ORC(r9, 0xff00, r9)
ANDC(r9, 0xff00, r9)
SHLC(r9, 16, r9)
ORC(r10, 0x00ff, r10)
SHLC(r10, 8, r10)
ORC(r10, 0x00ff, r10)
OR(r9, r10, r9)
BR(A4)
A3:
SHLC(r3, 24, r3)
ORC(r9, 0x00ff, r9)
SHLC(r9, 16, r9)
ORC(r10, 0x00ff, r10)
SHLC(r10, 8, r10)
ORC(r10, 0x00ff, r10)
OR(r9, r10, r9)
A4:
AND(r5, r9, r5)
OR(r5, r3, r5)
ST(r5, 0, r4)
restore_all_regs(regs)
JMP(xp)