S3C2440A RISC MICROPROCESSOR PROGRAMMER'S MODEL
2-7
Accessing Hi-Registers in THUMB State
In THUMB state, registers R8-R15 (“Hi registers”) are not part of the standard register set. However, the
assembly language programmer has limited access to them, and can use them for fast temporary storage.
A value may be transferred from a register in the range R0-R7 (a Lo register) to a Hi register and from a Hi register
to a Lo register, using special variants of the MOV instruction. Hi register values can also be compared agains t or
added to Lo register values with the CMP and ADD instructions. For more information, Please refer to Figure 3-34.
THE PROGRAM STATUS REGISTERS
The ARM920T contains a Current Program Status Register (CPSR), plus five Saved Program Status Registers
(SPSRs) for use by exception handlers. These register's functions are:
Hold information about the most recently performed ALU operation
Control the enabling and disabling of interrupts
Set the processor operating mode
The arrangement of bits is shown in Figure 2-6.
31
Condition Code Flags
Overflow
NZ C V I F T M4 M3 M2 M1 M0
30 29 2728 26252423 876543210
(Reserved) Control Bits
Carry/Borrow/Extend
Zero
Negative/Less Than
Mode bits
State bit
FIQ disable
IRQ disable
~
~~
~
Figure 2-6. Program Status Register Format