From ebdd572f8ee6493dd8e61d8d82c1d3ad5f10ac9f Mon Sep 17 00:00:00 2001
From: Liam Kerr <liam.d.kerr@protonmail.com>
Date: Fri, 1 May 2026 23:14:44 +0100
Subject: [PATCH] feat: implement basic timer

---
 src/kernel/interrupts.c |  6 +++---
 src/kernel/kernel.c     | 10 ++++++++++
 src/kernel/plic.c       |  8 +++++++-
 src/kernel/plic.h       |  1 +
 src/kernel/timer.c      | 39 +++++++++++++++++++++++++++++++++++++++
 src/kernel/timer.h      | 23 +++++++++++++++++++++++
 6 files changed, 83 insertions(+), 4 deletions(-)
 create mode 100644 src/kernel/timer.c
 create mode 100644 src/kernel/timer.h

diff --git a/src/kernel/interrupts.c b/src/kernel/interrupts.c
index 479e7c3..366f1c3 100644
--- a/src/kernel/interrupts.c
+++ b/src/kernel/interrupts.c
@@ -6,6 +6,8 @@
 #include <kernel/plic.h>
 #include <kernel/interrupts.h>
 #include <kernel/memory.h>
+#include <kernel/timer.h>
+
 
 void interrupt_init()
 {
@@ -111,9 +113,7 @@ void handle_interrupt(unsigned long code)
     switch (code)
     {
     case 7:
-        static volatile uint64_t *mtime = (uint64_t *)CLINT_MTIME;
-        static volatile uint64_t *mtimecmp = (uint64_t *)CLINT_MTIMECMP(0);
-        *mtimecmp = *mtime + 100000;
+        timer_tick();
         break;
     case 11:
         volatile uint32_t *claim_reg = (uint32_t *)PLIC_CLAIM(0);
diff --git a/src/kernel/kernel.c b/src/kernel/kernel.c
index 1d935c3..da2a669 100644
--- a/src/kernel/kernel.c
+++ b/src/kernel/kernel.c
@@ -5,11 +5,13 @@
 #include <kernel/plic.h>
 #include <kernel/interrupts.h>
 #include <kernel/memory.h>
+#include <kernel/timer.h>
 
 void kmain()
 {
     zero_bss();
     plic_init();
+    timer_init();
     uart_init();
     page_init();
     interrupt_init();
@@ -17,4 +19,12 @@ void kmain()
     kprintf("Hello, from %s!", "SquidgeOS");
     kputs("----------------------");
     knewline();
+    while (1) {
+        uint64_t ticks = timer_get_ms();
+        kputchar('T');
+        kputchar(':');  // Print "T:1234" every second
+        kprint_int(ticks);
+        knewline();
+        delay_ms(1000);
+    }
 }
diff --git a/src/kernel/plic.c b/src/kernel/plic.c
index 5a14838..86e6792 100644
--- a/src/kernel/plic.c
+++ b/src/kernel/plic.c
@@ -13,7 +13,13 @@ void plic_init()
     // This is a bitmask, so we shift 1 by the IRQ number.
     *PLIC_ENABLE(hart) = (1 << UART_IRQ);
 
+    // Set priority for CLINT timer interrupt (IRQ 5)
+    *PLIC_PRIORITY(TIMER_IRQ) = 1;  // Lowest priority
+
+    // Enable CLINT timer interrupt for Hart 0
+    *PLIC_ENABLE(hart) |= (1 << TIMER_IRQ);
+
     // 3. Set the priority threshold for Hart 0
     // We set this to 0 so that ANY interrupt with priority > 0 gets through.
     *PLIC_THRESHOLD(hart) = 0;
-}
\ No newline at end of file
+}
diff --git a/src/kernel/plic.h b/src/kernel/plic.h
index 9235164..3e72087 100644
--- a/src/kernel/plic.h
+++ b/src/kernel/plic.h
@@ -16,6 +16,7 @@
 #define PLIC_CLAIM(hart) ((volatile uint32_t *)(PLIC_BASE + 0x200004 + (hart) * 0x1000))
 
 #define UART_IRQ 10
+#define TIMER_IRQ 5
 
 void plic_init();
 
diff --git a/src/kernel/timer.c b/src/kernel/timer.c
new file mode 100644
index 0000000..2267aef
--- /dev/null
+++ b/src/kernel/timer.c
@@ -0,0 +1,39 @@
+#include <stdint.h>
+#include "timer.h"
+#include "plic.h"
+#include "interrupts.h"
+
+_Atomic uint64_t sys_ticks = 0;
+const uint64_t tick_delta = 1000;
+
+void timer_init() {
+    timer_tick();
+}
+
+void timer_tick() {
+    // Set the first timer interrupt to fire after 1ms
+    static volatile uint64_t *mtime = (uint64_t *)CLINT_MTIME;
+    static volatile uint64_t *mtimecmp = (uint64_t *)CLINT_MTIMECMP(0);
+    *mtimecmp = *mtime + tick_delta;
+    sys_ticks++;
+}
+
+// Get current time in milliseconds
+uint64_t timer_get_ms() {
+    return sys_ticks;
+}
+
+// Delay for 'ms' milliseconds (blocking)
+void delay_ms(uint64_t ms) {
+    if (ms == 0) return;
+    uint64_t end = sys_ticks + ms;
+    while (sys_ticks < end) {
+        asm volatile("wfi");
+    }
+}
+
+// Sleep for 'ms' milliseconds (non-blocking, if possible)
+// For now, just call delay_ms (can be improved later)
+void sleep_ms(uint64_t ms) {
+    delay_ms(ms);
+}
\ No newline at end of file
diff --git a/src/kernel/timer.h b/src/kernel/timer.h
new file mode 100644
index 0000000..ac0a2af
--- /dev/null
+++ b/src/kernel/timer.h
@@ -0,0 +1,23 @@
+#ifndef TIMER_H
+#define TIMER_H
+#include <stdint.h>
+
+extern _Atomic uint64_t sys_ticks;
+extern const uint64_t tick_delta;
+
+// Initialize timer (1ms ticks)
+void timer_init();
+
+// Increment the system tick counter
+void timer_tick();
+
+// Get current time in milliseconds
+uint64_t timer_get_ms();
+
+// Delay for 'ms' milliseconds (blocking)
+void delay_ms(uint64_t ms);
+
+// Sleep for 'ms' milliseconds (non-blocking, if possible)
+void sleep_ms(uint64_t ms);
+
+#endif
\ No newline at end of file