From 2725b95a1f78d2feac553d37252f2e560c2f9aac Mon Sep 17 00:00:00 2001
From: Carlos Maiolino <cem@toxiclabs.cc>
Date: Fri, 1 Aug 2025 21:03:16 +0200
Subject: Setup interrupt handling

Remap master PIC to IOAddress 0x20 to avoid collisions with CPU
exceptions.

Setup a default interrupt handler and map all interrupts to this handler
by default.

Setup a Keyboard interrupt handler for testing purposes

Wire everything up in the Makefile

Signed-off-by: Carlos Maiolino <cem@toxiclabs.cc>
---
 Makefile                |  6 +++++-
 src/boot/bootloader.asm |  4 +++-
 src/idt/idt.asm         | 24 +++++++++++++++++++++++-
 src/idt/idt.c           | 23 +++++++++++++++++++++++
 src/kernel.asm          | 13 +++++++++++++
 src/kernel.c            |  3 +++
 6 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 51493cd..040c846 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,8 @@ KOBJ_FILES = $(KERNEL_ASM_OBJ) \
 	     $(KERNEL_OBJ) \
 	     ./build/vga.o \
 	     ./build/idt/idt.asm.o \
-	     ./build/idt/idt.o
+	     ./build/idt/idt.o \
+	     ./build/io/io.asm.o
 
 
 BOOT_TGT =./bin/boot.bin
@@ -57,6 +58,8 @@ $(BUILD_DIR)/idt/idt.asm.o: ./src/idt/idt.asm
 $(BUILD_DIR)/idt/idt.o: ./src/idt/idt.c ./build/vga.o $(KOBJ_LIBS)
 	i686-elf-gcc $(INCLUDES) $(FLAGS) -std=gnu99 -c ./src/idt/idt.c -o $(BUILD_DIR)/idt/idt.o
 
+$(BUILD_DIR)/io/io.asm.o: ./src/io/io.asm
+	nasm -f elf -g ./src/io/io.asm -o $(BUILD_DIR)/io/io.asm.o
 
 $(KOBJ_LIBS):
 	i686-elf-gcc $(INCLUDES) $(FLAGS) -std=gnu99 -c ./src/lib/string.c -o $(BUILD_DIR)/string.o
@@ -70,4 +73,5 @@ clean:
 	rm -f build/string.o
 	rm -f build/idt/idt.asm.o
 	rm -f build/idt/idt.o
+	rm -f build/io/io.asm.o
 	rm -f bin/os.bin
diff --git a/src/boot/bootloader.asm b/src/boot/bootloader.asm
index 4b803fa..918ff9b 100644
--- a/src/boot/bootloader.asm
+++ b/src/boot/bootloader.asm
@@ -30,7 +30,9 @@ step2:
 	sti		; Enable interrupts
 
 .load_protected:
-	cli
+	cli	; Interrupts will be disabled until we finish setting up the interrupt
+		; table and remapping the PIC controllers
+		; Interrupts will be enabled back in _start symbol in kernel.asm
 	lgdt[gdt_table]
 	mov eax, cr0
 	or eax, 0x1
diff --git a/src/idt/idt.asm b/src/idt/idt.asm
index 998a242..235f46b 100644
--- a/src/idt/idt.asm
+++ b/src/idt/idt.asm
@@ -1,6 +1,12 @@
 section .asm
 
-global idt_load:
+extern int21h_handler
+extern default_int_handler
+
+global int21h
+global default_handler
+global idt_load
+
 
 idt_load:
 	push ebp
@@ -11,3 +17,19 @@ idt_load:
 
 	pop ebp
 	ret
+
+int21h:
+	cli
+	pushad	; Push all general-purpose registers to the stack
+	call int21h_handler
+	popad
+	sti
+	iret
+
+default_handler:
+	cli
+	pushad	; Push all general-purpose registers to the stack
+	call default_int_handler
+	popad
+	sti
+	iret
diff --git a/src/idt/idt.c b/src/idt/idt.c
index d7a6743..a83c612 100644
--- a/src/idt/idt.c
+++ b/src/idt/idt.c
@@ -3,11 +3,28 @@
 #include <toxic/string.h>
 #include <toxic/vga.h>
 #include <toxic/idt.h>
+#include <toxic/io.h>
 
 struct int_descriptor int_table[TOTAL_INTERRUPTS];
 struct int_reg_descriptor idtr_descriptor;
 
 extern void idt_load(struct int_reg_descriptor *desc);
+extern void int21h();
+extern void default_handler();
+
+void
+int21h_handler(void)
+{
+	vprintl("Keyboard pressed\n");
+	outb(0x20, 0x20);
+}
+
+void
+default_int_handler(void)
+{
+	/* Ack the Interrupt */
+	outb(0x20, 0x20);
+}
 
 static void
 idt_zero()
@@ -30,12 +47,18 @@ idt_set(int int_num, void *addr)
 void
 interrupts_init(void)
 {
+	int i;
+
 	memset(int_table, 0, sizeof(int_table));
 
 	idtr_descriptor.limit = sizeof(int_table) - 1;
 	idtr_descriptor.base = (uint32_t) int_table;
 
+	for (i = 0; i < TOTAL_INTERRUPTS; i++)
+	       idt_set(i, default_handler);
+
 	idt_set(0, idt_zero);
+	idt_set(0x21, int21h);
 
 	idt_load(&idtr_descriptor);
 }
diff --git a/src/kernel.asm b/src/kernel.asm
index 252fd7b..bd22761 100644
--- a/src/kernel.asm
+++ b/src/kernel.asm
@@ -24,6 +24,19 @@ _start:
 	or al, 2
 	out 0x92, al
 
+
+	; Remap master PIC
+	mov al, 00010001b
+	out 0x20, al	; MasterPIC
+
+	mov al, 0x20	; Start master ISR at 0x20
+	out 0x21, al
+
+	mov al, 00000001b	; Put the PIC in x86 mode
+	out 0x21, al
+
+	sti
+
 	; Jump to C code
 	call start_kernel
 	jmp $
diff --git a/src/kernel.c b/src/kernel.c
index c2a0150..8a8bd61 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -4,11 +4,14 @@
 #include <toxic/string.h>
 #include <toxic/kernel.h>
 #include <toxic/idt.h>
+#include <toxic/io.h>
 
 void start_kernel()
 {
 	init_display(2);
 	vprintl("Hello World!!!\n");
+	vprintl("Testing it!!!\n");
 
 	interrupts_init();
+
 }
-- 
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