From e087746a5d39370d7232a80087523a014a01e877 Mon Sep 17 00:00:00 2001 From: babbleberry Date: Tue, 6 Feb 2024 12:16:07 +0000 Subject: [PATCH] Updated README for part13-interrupts --- part13-interrupts/README.md | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/part13-interrupts/README.md b/part13-interrupts/README.md index b865475..e4e6249 100644 --- a/part13-interrupts/README.md +++ b/part13-interrupts/README.md @@ -35,6 +35,7 @@ The timers are set up using these calls: ```c irq_init_vectors(); enable_interrupt_controller(); +irq_barrier(); irq_enable(); timer_init(); ``` @@ -77,7 +78,7 @@ In the middle we simply call a function called `handle_irq()` which is written i void handle_irq() { 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) { 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: +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 .globl irq_enable irq_enable: @@ -129,6 +132,11 @@ irq_enable: irq_disable: msr daifset, #2 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...!