Basic Timer Interrupt

Makefile

@@ -36,7 +36,7 @@ $(OUT_DIR)start.o: kernel/start.s
 # Pattern rule for any .c → build/*.o
 $(OUT_DIR)%.o: %.c
 	@mkdir -p $(OUT_DIR)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(CFLAGS) -c $< -o $@ $(KFLAGS) # KFLAGS is used for custom kernel flags
 
 # Link everything
 $(OUT_DIR)kernel.elf: $(OUT_DIR)start.o $(OBJS) kernel.ld

README.md

@@ -34,6 +34,11 @@ Make sure you have an ARM cross-compiler installed (e.g., `arm-none-eabi-gcc`) a
 make
 ```
 
+Developers also have the option to run the kernel with custom flags such as:
+```sh
+make KFLAGS="-USE_KTESTS -MY_DEFFLAG"
+```
+
 > [!IMPORTANT]
 > 
 > `make` will clean, build, and run the kernel in QEMU. You can also run 
@@ -64,4 +69,4 @@ For more details about this kernel, refer to the [AstraKernel Documentation](htt
 
 ## License
 
-This project is licensed under the GNU GENERAL PUBLIC License. See the [LICENSE](LICENSE) file for details.
+This project is licensed under the GNU GENERAL PUBLIC License. See the [LICENSE](LICENSE) file for details.

include/interrupt.h

@@ -0,0 +1,56 @@
+#ifndef INTERRUPT_H
+#define INTERRUPT_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+// PL190 VIC (interrupt controller)
+// ref: PrimeCell Vectored Interrupt Controller (PL190) TRM (Page3-7)
+#define VIC_BASE        0x10140000u
+#define VIC_INTSELECT   (*(volatile uint32_t *)(VIC_BASE + 0x00C)) // 0=IRQ,1=FIQ
+#define VIC_INTENABLE   (*(volatile uint32_t *)(VIC_BASE + 0x010)) // set bit=enable
+#define VIC_INT_ENCLR   (*(volatile utin32_t *)(VIC_BASE + 0x014))
+#define VIC_SOFT_INT    (*(volatile uint32_t *)(VIC_BASE + 0x018))
+#define VIC_SOFT_INTCLR (*(volatile uint32_t *)(VIC_BASE + 0x01C))
+
+// SP804 Timer0 in the 0/1 block
+// ref: ARM Dual-Time Module (SP804) TRM (Page 3-2)
+#define T01_BASE    0x101E2000u
+#define T0_LOAD     (*(volatile uint32_t *)(T01_BASE + 0x00))
+#define T0_VALUE    (*(volatile uint32_t *)(T01_BASE + 0x04))
+#define T0_CONTROL  (*(volatile uint32_t *)(T01_BASE + 0x08))
+#define T0_INTCLR   (*(volatile uint32_t *)(T01_BASE + 0x0C))
+#define T0_MIS      (*(volatile uint32_t *)(T01_BASE + 0x14))
+
+// Bits for CONTROL (SP804)
+// ref: ARM Dual-Time Module (SP804) TRM (Page 3-5)
+#define TCTRL_ENABLE    (1u << 7)   // EN=bit7
+#define TCTRL_PERIODIC  (1u << 6)   // PERIODIC=bit6
+#define TCTRL_INTEN     (1u << 5)   // INTEN=bit5
+#define TCTRL_32BIT     (1u << 1)   // 32BIT=bit1
+
+// VIC line number for Timer0/1 on Versatile
+#define IRQ_TIMER01 4
+
+    static inline void timer0_start_periodic(uint32_t load)
+    {
+        T0_CONTROL  = 0;        // disable while reconfig
+        T0_LOAD     = load;     // ex: 10000 for ~100 Hz if TIMCLK≈1 MHz
+        T0_INTCLR   = 1;        // clear any pending interrupt
+        T0_CONTROL  = TCTRL_32BIT | TCTRL_PERIODIC | TCTRL_INTEN | TCTRL_ENABLE;
+    }
+
+    static inline void vic_enable_timer01_irq(void)
+    {
+        VIC_INTSELECT   &= ~(1u << IRQ_TIMER01);  // route to IRQ
+        VIC_INTENABLE   |=  (1u << IRQ_TIMER01);  // enable line 4
+    }
+#ifdef __cplusplus
+}
+#endif
+
+#endif // INTERRUPT_H

kernel/irq.c

@@ -1,11 +1,13 @@
 #include <stdint.h>
 
 #include "irq.h"
+#include "interrupt.h"
 
 volatile unsigned int tick = 0;
 
 void irq_handler(void)
 {
+    T0_INTCLR = 1; // this ack/clear the device (SP804)
     tick++;
 }
 

kernel/kernel.c

@@ -6,6 +6,7 @@
 #include "clear.h"
 #include "string.h"
 #include "irq.h"
+#include "interrupt.h"
 
 
 static const char *banner[] = {
@@ -54,7 +55,30 @@ void irq_sanity_check(void)
     }
 }
 
+// This function is for testing purposes.
+// It test that the timer interrupt is firing as expected.
+void not_main(void)
+{
+    puts("Time0 IRQ firing test!\r\n");
+
+    vic_enable_timer01_irq();
+    timer0_start_periodic(10000);
+    irq_enable();
+
+    unsigned last = 0;
+    for (;;)
+    {
+        unsigned n = tick;
+        if (n != last && (n % 100) == 0)
+        {
+            puts(".");
+            last = n;
+        }
+    }
+}
+
 /* The following macros are for testing purposes. */
+#define TIMER_TICK_TEST     not_main()
 #define SANITY_CHECK        irq_sanity_check()
 #define CALL_SVC_0          __asm__ volatile ("svc #0")
 
@@ -63,9 +87,12 @@ void kernel_main(void)
 {
     clear();
 
-    /* TEST */
+/* TESTS */
+#ifdef USE_KTESTS 
     SANITY_CHECK;
     CALL_SVC_0;
+    TIMER_TICK_TEST;
+#endif
 
     /* Back to normal operations */
     init_message();