Compilation and interrupt

MISP compilation

0.5 Common Operators

• add $r10, $r1, $r2 Showr10 = r1+r2
• addi $r1, $zero, 1000Show0寄存器和立即数1000相加放入r1
• lw $r0, 8($sp) Showload word sp地址+8 到r0
• beq $r3, $r9, LABELIndicate branch equalif they are equal, jump LABEL
• loadLoaded from memory register
• storeStorage back
• Math addi, subi, divi,multi
• sltIndicate set if less thanif less than execution
  • slt $d, $rs, $rt
  • slit $d, $rs, 5
• j LABEL Addressing LABEL
• jr $a0 Register Addressing
• jal LABELJump-one
  • The current PC + 4 is stored in the register $ ra
  • j LABELreturn

For example

1. Analyzing summation

if(i == j) {
    f = i + j
} else {
    f = i - j
}

compilation

bne $r3, $r4, ELSE # bne——branch not equal
add $r5, $r3, $r4
j EXIT # j——jump
ELSE:
sub $r5, $r3, $r4
EXIT

2.for loop

sum = 0
for(i = 0; i < 100; i++) {
    sum += i
}

compilation

addi $s3, $zero, 0 # sum = 0
addi $s4, $zero, 0 # i = 0
addi $s5, $zero, 100 # 100
LOOP:
beq $s4, $5, EXIT
add $s3, $s4, $s3
addi $s4, $s4, 1
j LOOP # -16
EXIT:

3. Functions

• Function body --Label label
• jal-- jump and link (jump and link)
• Parameter passing - Stack

# fac(5)
addiu $s0, $0, 5 # 函数参数5存入栈 add immidiate unsigned
sw $s0, $sp # s0写入sp
addi $sp, $sp, -4 # 栈指针指向下一个
jal FACT # 跳转

# 函数体
lw $s0, 4($sp) # 读取参数

4. The function returns

# 函数体最前面
sw $ra, 0$(sp)
addiu $sp, $sp, -4
lw $t1, 4($sp)
lw $s0, 8($sp)

jr $t1 # 跳转回去

Interrupt

When the outside world changes, attention occurred some time by interrupting the CPU. This time, the state executed by the CPU is stored, the interrupt program is executed

• OS loaded when you load the IVT (such as Type 01 program, interrupt response procedures exist on 0x003)
• Hardware interrupts - mouse, keyboard response actions
• Software interrupt - level language exception handling

Q&A

• 32 machine-interrupted path (ISR) only four bytes, how to perform the procedure?
  • Operating system interrupts, and then run the program
• How Key interrupt response path to the operating system and then to the application, the system knows?
  • Each keyboard is an address mapping
• error? Why not just jump error handling?
  • Not one relationship, to reduce the degree of coupling