Hi
I am new TO ARM7 And KEIL uVISION4 IDE.
I am using AT91FR40162S ATMEL COntroller.
When i created a project using KEIL IDE and selected AT91FR40162S ATMEL COntroller from the device list. Automatically startup.s file is added to the project.
In startup.s file Interrupts are Enabled and Disabled by following assembly code:
To Disable the interrupts
I_Bit EQU 0x80 ; when I bit is set, IRQ is disabled F_Bit EQU 0x40 ; when F bit is set, FIQ is disabled
; Enter Undefined Instruction Mode and set its Stack Pointer
MSR CPSR_c, #Mode_UND:OR:I_Bit:OR:F_Bit so interrupts are disabled here as corresponding bits in CPSR are set.
To Enable the interrupts
; Enter User Mode and set its Stack Pointer MSR CPSR_c, #Mode_USR
So interrupts are enabled
then after all the settings in startup.s it will jump to main.c file
QUESTION:
1. I want to enable and disable the interrupts in my main.c file. So How will i be able to access the CPSR register in my c coding.
Maybe: Using the Inline and Embedded Assemblers http://www.keil.com/support/man/docs/armcc/armcc_cihffbgf.htm
The use of inline and embedded assembler is somewhat restricted concerning the use of special registers like CPSR and SP. I recommend the use of plain assembler. Example for file intendis.s:
EXPORT DisableInterrupts EXPORT EnableInterrupts AREA ||.text||, CODE, READONLY, ALIGN=3 ARM PRESERVE8 DisableInterrupts PROC STMDB SP!, {R0} ; Push R0 MRS R0, CPSR ; Get CPSR. ORR R0, R0, #0xC0 ; Disable IRQ, FIQ. MSR CPSR_cxsf, R0 ; Write back modified value. LDMIA SP!, {R0} ; Pop R0 BX LR ; return ENDP EnableInterrupts PROC STMDB SP!, {R0-R1} ; Push R0,R1 MRS R0, CPSR ; Get CPSR. AND R1, R0, #0x0000001f ; R1 = R0 & 0x1f (mode bits) CMP R1, #0x00000012 ; Test for IRQ mode BICNE R0, R0, #0x80 ; Enable IRQ, but not in IRQ-Mode (no nesting) MSR CPSR_cxsf, R0 ; Write back modified value. LDMIA SP!, {R0-R1} ; Pop R0,R1 BX LR ; return ENDP END ; End of file
Of cause you need a header file intendis.h then:
#ifndef INTENDIS_H #define INTENDIS_H // this pair of functions has the following characteristics: // - disables all ints // - enables only IRQ, but not during interrupt service void DisableInterrupts(void); void EnableInterrupts(void); #endif /* INTENDIS_H */
Hope that helps.
Martin
I agree with the statement about inline assembler, but in which way is embedded assembler restricted?
But to answer the original question: > I want to enable and disable the interrupts in my main.c file. So How will i be able > to access the CPSR register in my c coding.
Two ways (both require running in privileged mode, of course):
1. Use compiler intrinsics __disable_irq()/__disable_fiq() and __enable_irq()/__enable_fiq() 2. Use named register variables (see manual)
Hope this helps -- Marcus http://www.doulos.com/arm/
Thanx a Lot Martin
I got the idea from ur code. But i need to be in supervisor mode to alter the CPSR register.
When i entered to the main function i was in USR mode so was not able to alter the CPSR register.
I want to know if i am in USR mode in my application main.c then if i want to change the CPSR register i need to change the MODE to SUPERVISOR mode.
So To alter CPSR bits How to change from USR mode to SUPERVISOR mode.
Thanx a lot in advance
Thanx a lot Marcus
From ur help also i got a clear idea. it works fine if i am in privileged mode.
My question is If I am in not privileged mode, How to change to privileged mode.
If i am in USR mode i can not alter CPSR bits so can not change SUPERVISOR mode from USR mode .
Thanx a lot Marcus and John also for responding so quickly
TO Marcus -
From ur help also i got a clear idea. it works fine if my code is running in privileged mode.
My question is If my code is not running in non privileged mode, How to change to privileged mode?
If my code is running in USR mode i can not alter CPSR bits so can not change MODE from USR to SUPERVISOR.
So how to change the mode from USR to SUPERVISOR.
Thanx In Advance
> So how to change the mode from USR to SUPERVISOR.
Have a look at the SVC instruction.
-- Marcus