Transcript Chapter 13

Chapter 13
ARM Exception Handling
(Real-Time Embedded Multithreading : Using ThreadX® and ARM®)
Department of Computer Science Hsu Hao Chen
Professor Hsung-Pin Chang
Outline
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Exception Resulting for ARM
Exception (Actions)
Reset Vector Initialization
ThreadX Initialization
Thread Scheduling
ThreadX Interrupt Handling
Internal Interrupt Processing
Exception Resulting for ARM
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Exceptions resulting for the direct effect
of executing an instruction
Exceptions resulting as a side effect of
executing an instruction
Exceptions resulting from external
interrupts, unrelated to instruction
execution
Exception (Actions) (1/2)
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Step 1:
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Step 2:
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Modify the CPSR of the new operating mode
Step 4:
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Change to the operating mode corresponding to
the exception
Step 3:
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Save CPSR -> SPSR
Save r15(PC) register -> r14(LR) register
Step 5:
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Change the PC to the appropriate exception vector
Exception (Actions) (2/2)
Reset Vector Initialization(1/2)
Reset Vector Initialization(2/2)
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LDR pc,=__my_low_level_init
branch (jump) or load PC
ThreadX Initialization(1/2)
Note: any code after tx_kernel_enter will never be executed
ThreadX Initialization(2/2)
tx_kernel_enter
_tx_initialize_low_level
tx_application_define
_tx_thread_schedule
Thread Scheduling
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Recovering thread context
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Solicited context
Interrupt context
Saving thread context
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_tx_thread_system_return
Solicited Context
extremely small(48 bytes of stack space)
Interrupt Context
Example :ARM code fragment(1/6)
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Example :ARM code fragment(3/6)
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Example :ARM code fragment(4/6)
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Example :ARM code fragment(5/6)
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LDMIA sp!, {r0,r1}
IA: Increment After
IB: Increment Before
DA: Decrement After
DB: Decrement Before
//r0= *sp!
//r1= *(sp!+4)
Example :ARM code fragment(6/6)
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MSRNE
SPSR_cxsf, r1 //copy r1->SPSR_cxsf
NE: Not equal
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BX lr
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Mov
//branch (jump) to lr
pc, lr
//copy lr->pc
ThreadX Interrupt Handling
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IRQ interrupt handling
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LDR pc, =__tx_irq_handler
FIQ interrupt handling
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LDR pc, =__tx_fiq_handler
Example Of A ThreadX IRQ Handler
Example Of A ThreadX FIQ Handler
Internal Interrupt Processing
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Idle system
Saving solicited thread contexts
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_tx_thread_context_save
Saving interrupt thread contexts
Nested interrupt handling
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Enable and disable nesting for IRQ interrupt
handlers
Enable and disable nesting for FIQ interrupt
handlers
Enable And Disable Nesting For IRQ Interrupt Handlers
EXPORT __tx_irq_handler
EXPORT __tx_irq_processing_return
__tx_irq_handler
B _tx_thread_context_save
__tx_irq_processing_return
BL _tx_thread_irq_nesting_start
BL
application_irq_handler
BL _tx_thread_irq_nesting_end
B _tx_thread_context_restore
Enable And Disable Nesting For FIQ Interrupt Handlers
EXPORT __tx_fiq_handler
EXPORT __tx_fiq_processing_return
__tx_fiq_handler
B _tx_thread_fiq_context_save
__tx_fiq_processing_return
BL _tx_thread_fiq_nesting_start
BL application_fiq_handler
BL _tx_thread_fiq_nesting_end
B _tx_thread_fiq_context_restore