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May 31, 2017 03:40
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Context switch on an interrupt vector
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| void __attribute__((interrupt("IRQ"))) _c_interrupt_vector(void) | |
| { | |
| static int lit = 0; | |
| /* Clear the ARM Timer interrupt - it's the only interrupt we have | |
| enabled, so we want don't have to work out which interrupt source | |
| caused us to interrupt */ | |
| RPI_GetArmTimer()->IRQClear = 1; | |
| /* Flip the LED */ | |
| if( lit ) | |
| { | |
| LED_OFF(); | |
| lit = 0; | |
| } | |
| else | |
| { | |
| LED_ON(); | |
| lit = 1; | |
| } | |
| } |
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| // To keep this in the first portion of the binary. | |
| .section ".text.boot" | |
| // External values | |
| .extern __irq_stack_top | |
| .extern __fiq_stack_top | |
| .extern __c_stack_top | |
| // Make globals. | |
| .global _start | |
| .global _get_stack_pointer | |
| .global _exception_table | |
| .global _enable_interrupts | |
| // From the ARM ARM (Architecture Reference Manual). Make sure you get the | |
| // ARMv5 documentation which includes the ARMv6 documentation which is the | |
| // correct processor type for the Broadcom BCM2835. The ARMv6-M manuals | |
| // available on the ARM website are for Cortex-M parts only and are very | |
| // different. | |
| // | |
| // See ARM section A2.2 (Processor Modes) | |
| .equ CPSR_MODE_USER, 0x10 | |
| .equ CPSR_MODE_FIQ, 0x11 | |
| .equ CPSR_MODE_IRQ, 0x12 | |
| .equ CPSR_MODE_SVR, 0x13 | |
| .equ CPSR_MODE_ABORT, 0x17 | |
| .equ CPSR_MODE_UNDEFINED, 0x1B | |
| .equ CPSR_MODE_SYSTEM, 0x1F | |
| // See ARM section A2.5 (Program status registers) | |
| .equ CPSR_IRQ_INHIBIT, 0x80 | |
| .equ CPSR_FIQ_INHIBIT, 0x40 | |
| .equ CPSR_THUMB, 0x20 | |
| _start: | |
| ldr pc, _reset_h | |
| ldr pc, _undefined_instruction_vector_h | |
| ldr pc, _software_interrupt_vector_h | |
| ldr pc, _prefetch_abort_vector_h | |
| ldr pc, _data_abort_vector_h | |
| ldr pc, _unused_handler_h | |
| ldr pc, _interrupt_vector_h | |
| ldr pc, _fast_interrupt_vector_h | |
| _reset_h: .word _reset_ | |
| _undefined_instruction_vector_h: .word _c_undefined_instruction_vector | |
| _software_interrupt_vector_h: .word _c_software_interrupt_vector | |
| _prefetch_abort_vector_h: .word _c_prefetch_abort_vector | |
| _data_abort_vector_h: .word _c_data_abort_vector | |
| _unused_handler_h: .word _reset_ | |
| _interrupt_vector_h: .word _interrupt_vector_ | |
| _fast_interrupt_vector_h: .word _c_fast_interrupt_vector | |
| _reset_: | |
| // We enter execution in supervisor mode. For more information on | |
| // processor modes see ARM Section A2.2 (Processor Modes) | |
| mov r0, #0x8000 | |
| mov r1, #0x0000 | |
| ldmia r0!,{r2, r3, r4, r5, r6, r7, r8, r9} | |
| stmia r1!,{r2, r3, r4, r5, r6, r7, r8, r9} | |
| ldmia r0!,{r2, r3, r4, r5, r6, r7, r8, r9} | |
| stmia r1!,{r2, r3, r4, r5, r6, r7, r8, r9} | |
| // IRQ Stack Pointer | |
| mov r0, #(CPSR_MODE_IRQ | CPSR_IRQ_INHIBIT | CPSR_FIQ_INHIBIT ) | |
| msr cpsr_c, r0 | |
| ldr sp, =__irq_stack_top | |
| // FRQ Stack Pointer | |
| mov r0, #(CPSR_MODE_FIQ | CPSR_IRQ_INHIBIT | CPSR_FIQ_INHIBIT ) | |
| msr cpsr_c, r0 | |
| ldr sp, =__fiq_stack_top | |
| // Service Mode Stack Pointer (C program) | |
| mov r0, #(CPSR_MODE_SVR | CPSR_IRQ_INHIBIT | CPSR_FIQ_INHIBIT ) | |
| msr cpsr_c, r0 | |
| ldr sp, =__c_stack_top | |
| // Startup C | |
| bl _c_startup | |
| // If main does return for some reason, just catch it and stay here. | |
| _inf_loop: | |
| b _inf_loop | |
| _get_stack_pointer: | |
| // Return the stack pointer value | |
| str sp, [sp] | |
| ldr r0, [sp] | |
| // Return from the function | |
| mov pc, lr | |
| _enable_interrupts: | |
| mrs r0, cpsr | |
| mov r1, #CPSR_IRQ_INHIBIT | |
| bic r0, r0, r1 | |
| msr cpsr_c, r0 | |
| // Return from the function | |
| mov pc, lr | |
| _interrupt_vector_: | |
| // Save current process context in process stack | |
| msr cpsr_c, #(CPSR_MODE_SVR | CPSR_IRQ_INHIBIT) | |
| stmfd sp!, {r0 - r3, ip, lr} | |
| // Save lr_irq and spsr_irq in process stack | |
| msr cpsr_c, #(CPSR_MODE_SVR | CPSR_IRQ_INHIBIT) | |
| sub lr, lr, #4 | |
| mov r1, lr | |
| mrs r2, spsr | |
| msr cpsr_c, #(CPSR_MODE_SVR | CPSR_IRQ_INHIBIT) | |
| stmfd sp!, {r1, r2} | |
| // Dispatch the interrupt to platform | |
| bl _c_interrupt_vector | |
| // Restore lr_irq and spsr_irq from process stack | |
| ldmfd sp!, {r1, r2} | |
| msr cpsr_c, #(CPSR_MODE_IRQ | CPSR_IRQ_INHIBIT) | |
| stmfd sp!, {r1} | |
| msr spsr_cxsf, r2 | |
| // Restore process regs | |
| msr cpsr_c, #(CPSR_MODE_IRQ | CPSR_IRQ_INHIBIT) | |
| ldmfd sp!, {r0 - r3, ip, lr} | |
| // Exit from IRQ | |
| msr cpsr_c, #(CPSR_MODE_IRQ | CPSR_IRQ_INHIBIT) | |
| ldmfd sp!, {pc}^ |
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