Programmer’s Model
2-8 Copyright © 2005-2008 ARM Limited. All rights reserved. ARM DDI 0337G
Non-Confidential
Unrestricted Access
Note
Because the ICI field and the IT field overlap, load or store multiples within an If-Then
block cannot be interrupt-continued.
Figure 2-4 shows the bit assignments of the EPSR.
Figure 2-4 Execution Program Status Register
The EPSR is not directly accessible. Two events can modify the EPSR:
• an interrupt occurring during an LDM or STM instruction
• execution of the If-Then instruction.
Table 2-3 describes the bit assignments of the EPSR.
31 0
Reserved Reserved
27 26 25 24 16 15 10 9
ReservedICI/IT ICI/IT
23
T
Table 2-3 Bit functions of the EPSR
Field Name Definition
[31:27] - Reserved.
[26:25], [15:10] ICI Interruptible-continuable instruction bits. When an interrupt occurs during an LDM or STM
operation, the multiple operation stops temporarily. The EPSR uses bits [15:12] to store the
number of the next register operand in the multiple operation. After servicing the interrupt,
the processor returns to the register pointed to by [15:12] and resumes the multiple
operation.
[26:25], [15:10] IT If-Then bits. These are the execution state bits of the If-Then instruction. They contain the
number of instructions in the if-then block and the conditions for their execution.
[24] T The T-bit can be cleared using an interworking instruction where bit [0] of the written PC
is 0. It can also be cleared by unstacking from an exception where the stacked T bit is 0.
Executing an instruction while the T bit is clear causes an INVSTATE exception.
[23:16] - Reserved.
[9:0] - Reserved.
To Next Page
Loading...
Need help?
General
