add timer driver and testcase

sw/examples/interrupt/Makefile.include

@@ -0,0 +1,2 @@
+src_files = interrupt.c
+executable = interrupt.elf

sw/examples/interrupt/interrupt.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <arch.h>
+#include <timer.h>
+
+#define TIMER_INTERRUPT_DELAY 1000
+
+void timer_interrupt_handler(){
+    // Clear interrupt
+    timer_clear_interrupt();
+    puts("!!! Caught timer interrupt !!!\n");
+}
+
+void setup_timer_interrupt() {
+    // Register Interrupt handler
+    register_interrupt_handler(7, timer_interrupt_handler);
+
+    // Request timer interrupt
+    timer_get_interrupt(TIMER_INTERRUPT_DELAY);
+
+    // Enable interrupts in core
+    arch_en_mti();
+    arch_en_int();
+}
+
+void main()
+{
+    serial_init(UART_BAUD_115200);
+    puts("Before interrupt\n");
+
+    setup_timer_interrupt();
+    asm volatile("wfi");        // wait for interrupt
+
+    puts("After interrupt\n");
+    return;
+}

sw/lib/include/timer.h

@@ -0,0 +1,8 @@
+#pragma once
+#include <stdint.h>
+
+uint64_t timer_get_time();
+
+void timer_get_interrupt(uint64_t time);
+
+void timer_clear_interrupt();

sw/lib/libcatom/hydrogensoc/timer.c

@@ -0,0 +1,27 @@
+#include <timer.h>
+#include <mmio.h>
+#include <platform.h>
+
+#define TIMER_REG_MTIME         0x0
+#define TIMER_REG_MTIMEH        0x4
+#define TIMER_REG_MTIMECMP      0x8
+#define TIMER_REG_MTIMECMPH     0xc
+
+uint64_t timer_get_time() {
+    uint64_t time = (uint64_t) REG32(TIMER_ADDR, TIMER_REG_MTIMEH);
+    time = (time << 32 ) | (uint64_t) REG32(TIMER_ADDR, TIMER_REG_MTIME);
+    return time;
+}
+
+void timer_get_interrupt(uint64_t time){
+    uint64_t curtime = (uint64_t) REG32(TIMER_ADDR, TIMER_REG_MTIMEH);
+    curtime = (curtime << 32 ) | (uint64_t) REG32(TIMER_ADDR, TIMER_REG_MTIME);
+    uint64_t exp_time = curtime + time;
+    REG32(TIMER_ADDR, TIMER_REG_MTIMECMPH) = 0xffffffff & (exp_time >> 32);
+    REG32(TIMER_ADDR, TIMER_REG_MTIMECMP) = 0xffffffff & exp_time;
+}
+
+void timer_clear_interrupt(){
+    REG32(TIMER_ADDR, TIMER_REG_MTIMECMPH) = (uint32_t)-1;
+    REG32(TIMER_ADDR, TIMER_REG_MTIMECMP) = (uint32_t)-1;
+}