Microprocessor learning notes # 1

Tips

The order of the notes may be disordered, according to your own thoughts and understanding, and will be sorted out later when there is time.

About ARM Thumb2 instruction set

The number of bytes in the instruction set

Most ARM Thumb2 instructions are 2 Bytes or half words, while some instructions nested with other instructions, such as the most common # instruction, require 4 Bytes or one word to store.
Special note : In general, 16 bits are used to represent, and a "bit" in hexadecimal is equivalent to 4 "bits" in binary, so for byte, one byte corresponds to binary The next 8 bits correspond to the next 2 bits in hexadecimal, and the half word size is 2byte, so half word needs to be represented by 4 hexadecimal "bits", and a word needs to be represented by 8 hexadecimal "bits.
Examples:

Assembly language	Address representation
MOV r0, #10	08000190: F0 4F 00 0A
LDR r2, [r1]	08000194: 68 11
ADD r0, r0, r2	08000196: 44 10

As can be seen from the above example, every two hexadecimal "bit" is a byte, so put together, every four bits is two bytes, that is, a half word, two half words form a word.

About the offset of the instruction

The offset of the instruction is obtained by the difference operation of the two instruction addresses, which is positive and negative, especially pay attention to the hexadecimal calculation, you can first subtract the small address from the large address and then determine the positive and negative.
Special note: The offset does not need to maintain the same 8-bit address as the command
Example:
0x08000190 + 0x1A-> 0x0800020A
0x0800020A-0x1A-> 0x08000190

Assembly language (C)

Common sentences

MOV can be used to assign
MOVS with carry
ADD addition
ADDS with carry
SUB subtraction
SUBS with carry
MUL multiplication
UDIV division
LDR load
STR storage

Control flow

if statement

void func(int a){
	if(a==0){
		a=1;
	}
}

compilation

void func(int a){
	CMP r0,#0
	BEQ CON1
COND1 
	MOVS r0,#1
	BX lr	
}

for statement

void func(int a)
{
	for(int i=0;i<5;i++){
		a--;
	}
}

compilation

void func(int a)
{
	MOVS r1,#0
LOOP
	CMP r1, #5
	BLS ENDLOOP
	ADDS r1,r1,#1
	SUBS r0,r0,#1
	B LOOP
ENDLOOP
	BX lr
}

while statement

void func(int a)
{
	while(a>0){
		a--;
	}
}

compilation

void func(int a)
{
LOOP
	CMP r0, #0
	BLT ENDLOOP
	SUBS r0,r0,#1
	B LOOP
ENDLOOP
	BX lr
}

To be continued. . .