/**
* @file
*
* @brief ARM interrupt exception prologue and epilogue.
*/
/*
* Copyright (c) 2009
* embedded brains GmbH
* Obere Lagerstr. 30
* D-82178 Puchheim
* Germany
* <rtems@embedded-brains.de>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.com/license/LICENSE.
*/
/*
* These two non-volatile registers contain the program status for INT and SVC
* mode. It is important that they are directly accessible in THUMB
* instruction mode.
*/
#define MODE_INT r4
#define MODE_SVC r5
/*
* These three non-volatile registers are used to exchange information between
* INT and SVC mode.
*/
#define SCRATCH_0 r6
#define SCRATCH_1 r7
#define SCRATCH_2 r8
/* List of scratch registers. They will be saved and restored in INT mode. */
#define SCRATCH_LIST {SCRATCH_0, SCRATCH_1, SCRATCH_2}
/*
* List of all volatile registers (r0, r1, r2, r3, r12 and lr), registers
* containing the interrupt context (return address in SCRATCH_0 and saved
* program status in SCRATCH_1) and non-volatile registers used for modes
* (MODE_INT and MODE_SVC). They will be saved and restored in SVC mode.
*/
#define TASK_CONTEXT_LIST \
{r0, r1, r2, r3, MODE_INT, MODE_SVC, SCRATCH_0, SCRATCH_1, r12, lr}
/*
* List of all volatile registers (r0, r1, r2, r3, r12 and lr) and the saved
* program status (SCRATCH_0 register). They will be saved and restored in INT
* mode.
*/
#define INTERRUPT_CONTEXT_LIST \
{r0, r1, r2, r3, SCRATCH_0, r12, lr}
.extern _ISR_Thread_dispatch
.extern _ISR_Nest_level
.extern _Thread_Dispatch_disable_level
.extern bsp_interrupt_dispatch
.arm
.globl arm_exc_interrupt
arm_exc_interrupt:
/* Save scratch registers on INT stack */
stmdb sp!, SCRATCH_LIST
/* Increment interrupt nest level */
ldr SCRATCH_0, =_ISR_Nest_level
ldr SCRATCH_1, [SCRATCH_0]
add SCRATCH_2, SCRATCH_1, #1
str SCRATCH_2, [SCRATCH_0]
/* Branch for nested interrupts */
cmp SCRATCH_1, #0
bne nested_interrupt_context_save
/* Move interrupt context and CPSR to scratch registers */
mov SCRATCH_0, lr
mrs SCRATCH_1, spsr
mrs SCRATCH_2, cpsr
/* Switch to SVC mode */
orr SCRATCH_2, SCRATCH_2, #0x1
msr cpsr_c, SCRATCH_2
/* Save context on SVC stack */
stmdb sp!, TASK_CONTEXT_LIST
/* Save SVC mode program status to non-volatile register */
mov MODE_SVC, SCRATCH_2
/* Save INT mode program status to non-volatile register */
bic MODE_INT, MODE_SVC, #0x1
/* Switch to INT mode */
msr cpsr_c, MODE_INT
/* Restore scratch registers from INT stack */
ldmia sp!, SCRATCH_LIST
/*
* At this point the INT stack is in the exception entry state and
* contains no data for us. The context is saved on the SVC stack. We
* can easily switch modes via the registers MODE_INT and MODE_SVC
* which are valid through subroutine calls. We can use all volatile
* registers in both modes. Note that this comment describes the non
* nested interrupt entry. For a nested interrupt things are
* different, since we can save everything on the INT stack and there
* is no need to switch modes.
*/
task_context_save_done:
/* Switch to THUMB instructions if necessary */
#ifdef __thumb__
add r0, pc, #1
bx r0
.thumb
#endif /* __thumb__ */
/* Increment thread dispatch disable level */
ldr r1, =_Thread_Dispatch_disable_level
ldr r3, [r1]
add r3, r3, #1
str r3, [r1]
/* Call BSP dependent interrrupt dispatcher */
bl bsp_interrupt_dispatch
/* Decrement interrupt nest and thread dispatch disable level */
ldr r0, =_ISR_Nest_level
ldr r1, =_Thread_Dispatch_disable_level
ldr r2, [r0]
ldr r3, [r1]
sub r2, r2, #1
sub r3, r3, #1
str r2, [r0]
str r3, [r1]
/* Switch to ARM instructions if necessary */
#ifdef __thumb__
.align 2
bx pc
.arm
#endif /* __thumb__ */
/* Branch if we have a nested interrupt */
cmp r2, #0
bne nested_interrupt_return
/* Branch if thread dispatching is disabled */
cmp r3, #0
bne thread_dispatch_done
/*
* Switch to SVC mode. It is important to call the thread dispatcher
* in SVC mode since overwise the INT stack may need to store an
* arbitrary number of contexts and it may lead to an invalid order of
* stack operations.
*/
msr cpsr_c, MODE_SVC
/* Call thread dispatcher */
#ifdef __thumb__
ldr r0, =_ISR_Thread_dispatch
mov lr, pc
bx r0
.thumb
bx pc
nop
.arm
#else
bl _ISR_Thread_dispatch
#endif
/* Switch to INT mode */
msr cpsr_c, MODE_INT
thread_dispatch_done:
/* Save scratch registers on INT stack */
stmdb sp!, SCRATCH_LIST
/* Switch to SVC mode */
msr cpsr_c, MODE_SVC
/* Move INT mode program status to scratch register */
mov SCRATCH_2, MODE_INT
/* Restore context from SVC stack */
ldmia sp!, TASK_CONTEXT_LIST
/* Switch to INT mode */
msr cpsr_c, SCRATCH_2
/* Restore interrupt context */
mov lr, SCRATCH_0
msr spsr, SCRATCH_1
/* Restore scratch registers from INT stack */
ldmia sp!, SCRATCH_LIST
/* Return from interrupt */
subs pc, lr, #4
nested_interrupt_context_save:
/* Move saved program status register to scratch register */
mrs SCRATCH_0, spsr
/* Save context on INT stack */
stmdb sp!, INTERRUPT_CONTEXT_LIST
b task_context_save_done
nested_interrupt_return:
/* Restore context from INT stack */
ldmia sp!, INTERRUPT_CONTEXT_LIST
/* Restore saved program status register */
msr spsr, SCRATCH_0
/* Restore scratch registers from INT stack */
ldmia sp!, SCRATCH_LIST
/* Return from interrupt */
subs pc, lr, #4
