os-workshop

commit 3b15f7a132033d76091d6c3096b15ab7a36f0180
parent 287dae4eb9d2945c6497426486676e5a8a0071f5
Author: Brian Swetland <swetland@frotz.net>
Date:   Thu, 12 May 2022 17:23:21 -0700

ex01-timer: periphierals, interrupts

Diffstat:
A
example/ex01-timer.c
 | 
72
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
project/ex01-timer.app.mk
 | 
6
++++++

2 files changed, 78 insertions(+), 0 deletions(-)
diff --git a/example/ex01-timer.c b/example/ex01-timer.c
@@ -0,0 +1,72 @@
+// Copyright 2022, Brian Swetland <swetland@frotz.net>
+// Licensed under the Apache License, Version 2.0
+
+#include <hw/riscv.h>
+#include <hw/context.h>
+#include <hw/debug.h>
+#include <hw/intrinsics.h>
+
+#include <hw/platform.h>
+#include <hw/litex.h>
+
+#define timer_rd(a) io_rd32(TIMER0_BASE + LX_TIMER_ ## a)
+#define timer_wr(a,v) io_wr32(TIMER0_BASE + LX_TIMER_ ## a, v)
+
+void timer_init(void) {
+	// disable, clear pending irqs
+	timer_wr(EN, 0);
+	timer_wr(EV_PENDING, LX_TIMER_EVb_ZERO);
+
+	// set for repeating every 100ms
+	timer_wr(LOAD, 0);
+	timer_wr(RELOAD, 50000000/10);
+
+	// enable timer and timer wrap irq
+	timer_wr(EN, 1);
+	timer_wr(EV_ENABLE, LX_TIMER_EVb_ZERO);
+}
+
+volatile uint32_t ticks = 0;
+
+void interrupt_handler(void) {
+	if (timer_rd(EV_PENDING)) {
+		timer_wr(EV_PENDING, LX_TIMER_EVb_ZERO);
+		ticks++;
+	}
+}
+
+void start(void) {
+	xprintf("Example 01 - Timer\n\n");
+
+	// set trap vector to trap_entry() in trap-entry-single.S
+	// it will call exception_handler() or interrupt_handler()
+	csr_write(CSR_STVEC, (uintptr_t) trap_entry);
+
+	// enable timer0 irq
+	csr_set(CSR_S_INTC_ENABLE, TIMER0_IRQb);
+
+	// enable external interrupts
+	csr_set(CSR_SIE, INTb_SVC_EXTERN);
+
+	// enable interrupts 
+	irq_enable();
+
+	timer_init();
+
+	while (1) {
+		uint32_t now = ticks;
+		xprintf("%02u:%02u.%1u\r", now/600, (now/10) % 60, now % 10);
+
+		// wait for ticks to change
+		while (now == ticks) ;
+	}
+}
+
+// if an exception occurs, dump register state and halt
+void exception_handler(eframe_t *ef) {
+	xprintf("\n** SUPERVISOR EXCEPTION **\n");
+	xprint_s_exception(ef);
+	xprintf("\nHALT\n");
+	for (;;) ;
+}
+
diff --git a/project/ex01-timer.app.mk b/project/ex01-timer.app.mk
@@ -0,0 +1,6 @@
+MOD_NAME := ex01-timer
+MOD_SRC := hw/src/start.S hw/src/trap-entry-single-stack.S
+MOD_SRC += example/ex01-timer.c
+MOD_SRC += hw/src/print-exception.c hw/src/debug-printf.c hw/src/debug-io.c
+MOD_LIB := c
+include make/app.mk