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Updated README for part13-interrupts

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babbleberry 2024-02-06 12:16:07 +00:00
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10
part13-interrupts/README.md
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@ -35,6 +35,7 @@ The timers are set up using these calls:
```c ```c
irq_init_vectors(); irq_init_vectors();
enable_interrupt_controller(); enable_interrupt_controller();
irq_barrier();
irq_enable(); irq_enable();
timer_init(); timer_init();
``` ```
@ -77,7 +78,7 @@ In the middle we simply call a function called `handle_irq()` which is written i
void handle_irq() { void handle_irq() {
unsigned int irq = REGS_IRQ->irq0_pending_0; unsigned int irq = REGS_IRQ->irq0_pending_0;
while(irq) { while(irq & (SYS_TIMER_IRQ_1 | SYS_TIMER_IRQ_3)) {
if (irq & SYS_TIMER_IRQ_1) { if (irq & SYS_TIMER_IRQ_1) {
irq &= ~SYS_TIMER_IRQ_1; irq &= ~SYS_TIMER_IRQ_1;
@ -119,6 +120,8 @@ Masking is a technique used by the CPU to prevent a particular piece of code fro
The `irq_enable` and `irq_disable` functions in _utils.S_ are responsible for masking and unmasking interrupts: The `irq_enable` and `irq_disable` functions in _utils.S_ are responsible for masking and unmasking interrupts:
They are helped by the `irq_barrier` function which ensures that the `enable_interrupt_controller()` call properly finishes before the `irq_enable()` call is made.
```c ```c
.globl irq_enable .globl irq_enable
irq_enable: irq_enable:
@ -129,6 +132,11 @@ irq_enable:
irq_disable: irq_disable:
msr daifset, #2 msr daifset, #2
ret ret
.globl irq_barrier
irq_barrier:
dsb sy
ret
``` ```
As soon as `irq_enable()` is called from `main()` in _kernel.c_, the timer handler is run when the timer interrupt fires. Well, sort of...! As soon as `irq_enable()` is called from `main()` in _kernel.c_, the timer handler is run when the timer interrupt fires. Well, sort of...!