+#include <stdio.h>
+#include "intr.h"
+#include "desc.h"
+#include "segm.h"
+#include "asmops.h"
+#include "panic.h"
+
+#define SYSCALL_INT 0x80
+
+/* IDT gate descriptor bits */
+#define GATE_TASK (5 << 8)
+#define GATE_INTR (6 << 8)
+#define GATE_TRAP (7 << 8)
+#define GATE_DEFAULT (1 << 11)
+#define GATE_PRESENT (1 << 15)
+
+/* PIC command and data ports */
+#define PIC1_CMD 0x20
+#define PIC1_DATA 0x21
+#define PIC2_CMD 0xa0
+#define PIC2_DATA 0xa1
+
+/* PIC initialization command word 1 bits */
+#define ICW1_ICW4_NEEDED (1 << 0)
+#define ICW1_SINGLE (1 << 1)
+#define ICW1_INTERVAL4 (1 << 2)
+#define ICW1_LEVEL (1 << 3)
+#define ICW1_INIT (1 << 4)
+/* PIC initialization command word 4 bits */
+#define ICW4_8086 (1 << 0)
+#define ICW4_AUTO_EOI (1 << 1)
+#define ICW4_BUF_SLAVE (1 << 3) /* 1000 */
+#define ICW4_BUF_MASTER (3 << 2) /* 1100 */
+#define ICW4_SPECIAL (1 << 4)
+
+/* PIC operation command word 2 bits */
+#define OCW2_EOI (1 << 5)
+
+
+static void init_pic(int offset);
+static void gate_desc(desc_t *desc, uint16_t sel, uint32_t addr, int dpl, int type);
+
+/* defined in intr_asm.S */
+void set_idt(uint32_t addr, uint16_t limit);
+void intr_entry_default(void);
+
+/* the IDT (interrupt descriptor table) */
+static desc_t idt[256] __attribute__((aligned(8)));
+
+/* table of handler functions for all interrupts */
+static intr_func_t intr_func[256];
+
+static struct intr_frame *cur_intr_frame;
+static int eoi_pending;
+
+
+void init_intr(void)
+{
+ int i;
+
+ set_idt((uint32_t)idt, sizeof idt - 1);
+
+ /* initialize all entry points and interrupt handlers */
+ for(i=0; i<256; i++) {
+ set_intr_entry(i, intr_entry_default);
+ interrupt(i, 0);
+ }
+
+ /* by including intrtab.h here (without ASM being defined)
+ * the series of INTR_ENTRY_* macros will be expanded to a series
+ * of function prototypes for all interrupt entry points and the
+ * corresponding calls to set_intr_entry to set up the IDT slots
+ */
+#include "intrtab.h"
+
+ /* initialize the programmable interrupt controller
+ * setting up the maping of IRQs [0, 15] to interrupts [32, 47]
+ */
+ init_pic(IRQ_OFFSET);
+ eoi_pending = 0;
+}
+
+/* retrieve the current interrupt frame.
+ * returns 0 when called during init.
+ */
+struct intr_frame *get_intr_frame(void)
+{
+ return cur_intr_frame;
+}
+
+/* set an interrupt handler function for a particular interrupt */
+void interrupt(int intr_num, intr_func_t func)
+{
+ intr_func[intr_num] = func;
+}
+
+/* this function is called from all interrupt entry points
+ * it calls the appropriate interrupt handlers if available and handles
+ * sending an end-of-interrupt command to the PICs when finished.
+ */
+void dispatch_intr(struct intr_frame frm)
+{
+ cur_intr_frame = &frm;
+
+ if(IS_IRQ(frm.inum)) {
+ eoi_pending = frm.inum;
+ }
+
+ if(intr_func[frm.inum]) {
+ intr_func[frm.inum](frm.inum);
+ } else {
+ if(frm.inum < 32) {
+ panic("unhandled exception %d, error code: %d\n", frm.inum, frm.err);
+ }
+ printf("unhandled interrupt %d\n", frm.inum);
+ }
+
+ disable_intr();
+ if(eoi_pending) {
+ end_of_irq(INTR_TO_IRQ(eoi_pending));
+ }
+}
+
+static void init_pic(int offset)
+{
+ /* send ICW1 saying we'll follow with ICW4 later on */
+ outb(ICW1_INIT | ICW1_ICW4_NEEDED, PIC1_CMD);
+ outb(ICW1_INIT | ICW1_ICW4_NEEDED, PIC2_CMD);
+ /* send ICW2 with IRQ remapping */
+ outb(offset, PIC1_DATA);
+ outb(offset + 8, PIC2_DATA);
+ /* send ICW3 to setup the master/slave relationship */
+ /* ... set bit3 = 3rd interrupt input has a slave */
+ outb(4, PIC1_DATA);
+ /* ... set slave ID to 2 */
+ outb(2, PIC2_DATA);
+ /* send ICW4 to set 8086 mode (no calls generated) */
+ outb(ICW4_8086, PIC1_DATA);
+ outb(ICW4_8086, PIC2_DATA);
+ /* done, just reset the data port to 0 */
+ outb(0, PIC1_DATA);
+ outb(0, PIC2_DATA);
+}
+
+static void gate_desc(desc_t *desc, uint16_t sel, uint32_t addr, int dpl, int type)
+{
+ /* first 16bit part is the low 16bits of the entry address */
+ desc->d[0] = addr & 0xffff;
+ /* second 16bit part is the segment selector for the entry code */
+ desc->d[1] = sel;
+ /* third 16bit part has the privilege level, type, and present bit */
+ desc->d[2] = ((dpl & 3) << 13) | type | GATE_DEFAULT | GATE_PRESENT;
+ /* last 16bit part is the high 16bits of the entry address */
+ desc->d[3] = (addr & 0xffff0000) >> 16;
+}
+
+#define IS_TRAP(n) ((n) >= 32 && !IS_IRQ(n))
+void set_intr_entry(int num, void (*handler)(void))
+{
+ int type = IS_TRAP(num) ? GATE_TRAP : GATE_INTR;
+
+ /* the syscall interrupt has to have a dpl of 3 otherwise calling it from
+ * user space will raise a general protection exception. All the rest should
+ * have a dpl of 0 to disallow user programs to execute critical interrupt
+ * handlers and possibly crashing the system.
+ */
+ int dpl = (num == SYSCALL_INT) ? 3 : 0;
+
+ gate_desc(idt + num, selector(SEGM_KCODE, 0), (uint32_t)handler, dpl, type);
+}
+
+void end_of_irq(int irq)
+{
+ int intr_state = get_intr_flag();
+ disable_intr();
+
+ if(!eoi_pending) {
+ return;
+ }
+ eoi_pending = 0;
+
+ if(irq > 7) {
+ outb(OCW2_EOI, PIC2_CMD);
+ }
+ outb(OCW2_EOI, PIC1_CMD);
+
+ set_intr_flag(intr_state);
+}
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