Load/store access instruction of arm instruction set (2)

This note records the second kind of Load/Store Instructions , That is, the operand is 16 Bit halfword and signed byte data Load/Store Instructions .

Mnemonic symbol	explain
LDRH	Half word data read instruction
STRH	Half word data write instruction
LDRSB	Signed byte data read instruction
LDRSH	Signed halfword data read instruction

Addressing mode

These instructions have a consistent way of addressing , See here .

	grammar	explain
1	[<Rn>, #+/-<offset_8>]	Immediate offset addressing
2	[<Rn>, +/-<Rm>]	Register offset addressing
3	[<Rn>, #+/-<offset_8>]!	Immediate pre update addressing
4	[<Rn>, #+/-<Rm>]!	Register pre update addressing
5	[<Rn>], #+/-<offset_8>	Immediate post update addressing
6	[<Rn>], +/-	Register post update addressing

LDRH( Half word data read instruction )

LDR{<cond>}H <Rd>, <address_mode>

if CondPassed(cond) then
	if address[0] == 0 then
		data = Mem[address, 2]
	else
		data =  Unknown 
	Rd = data

so , This instruction requires that the address must be half word aligned .

STRH( Half word data write instruction )

STR{<cond>}H <Rd>, <address_mode>

if CondPassed(cond) then
	if address[0] == 0 then
		data = Rd[15:0]
	else
		data =  Unknown 
	Mem[address, 2] = data

Again , This instruction requires that the address must be half word aligned .

LDRSB( Signed byte data read instruction )

LDRSB Read a byte of data from memory and save it in the low of the destination register 8 position , Then fill the high of the destination register according to the sign bits 24 position , This generates the final 32 digit .

LDR{cond}SB <Rd>, <address_mode>

if CondPassed(cond) then
	data = Mem[address, 1]
	Rd = SignExtend(data)

LDRSH( Signed halfword data read instruction )

LDRSH Read a half word data from memory and save it in the low of the target register 16 position , Then fill the high of the destination register according to the sign bits 16 position , This generates the final 32 digit .

LDR{<cond>}SH <Rd>, <address_mode>

if CondPassed(cond) then
	if address[0] == 0 then
		data = Mem[address, 2]
	else
		data =  Unknown 
	Rd = SignExtend(data)

Again , This instruction requires that the address must be half word aligned .