From c84d214daa507fdc267acfc92b0895b417c9553a Mon Sep 17 00:00:00 2001
From: Alexander Myltsev <a.myltsev@gmail.com>
Date: Wed, 25 Jan 2023 14:56:38 +0400
Subject: [PATCH] Add drivers/pit.c by 3Hren.

---
 Makefile      |  2 +-
 drivers/pit.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/pit.h |  8 ++++++
 kernel.c      |  7 +++++
 4 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 drivers/pit.c
 create mode 100644 drivers/pit.h

diff --git a/Makefile b/Makefile
index ab4d4f6..6593b63 100644
--- a/Makefile
+++ b/Makefile
@@ -76,7 +76,7 @@ image.bin: mbr.bin fs.img
 
 kernel.bin: kernel.o console.o drivers/vga.o drivers/keyboard.o \
 	drivers/ata.o cpu/vectors.o cpu/idt.o cpu/gdt.o drivers/uart.o \
-	fs/fs.o lib/mem.o lib/string.o proc.o cpu/swtch.o
+	fs/fs.o lib/mem.o lib/string.o proc.o cpu/swtch.o drivers/pit.o
 	$(LD) $(LDFLAGS) $(LDKERNELFLAGS) -o $@ -Ttext 0x1000 $^
 
 %.o: %.c
diff --git a/drivers/pit.c b/drivers/pit.c
new file mode 100644
index 0000000..7b8edc1
--- /dev/null
+++ b/drivers/pit.c
@@ -0,0 +1,76 @@
+#include "pit.h"
+#include "port.h"
+#include "../cpu/isr.h"
+
+enum {
+    PIT_CRYSTAL_HZ = 1193182,
+
+    CLOCK_PRECISION_HZ = 100,
+
+    PIT_PROGRAM_REG = PIT_CRYSTAL_HZ / CLOCK_PRECISION_HZ,
+
+    PIT_SELECT_CHANNEL0 = 0x0,
+    PIT_SELECT_CHANNEL1 = 0x1,
+    PIT_SELECT_CHANNEL2 = 0x2,
+    PIT_SELECT_CHANNEL_RB = 0x3,
+    PIT_ACCESS_MODE_LATCH_COUNT_VALUE_COMMAND = 0x0,
+    PIT_ACCESS_MODE_LOBYTE_ONLY = 0x1,
+    PIT_ACCESS_MODE_HIBYTE_ONLY = 0x2,
+    PIT_ACCESS_MODE_LOHIBYTE = 0x3,
+    PIT_MODE_INTERRUPT_ON_TERMINAL_COUNT = 0x0,
+    PIT_MODE_HW_ONESHOT = 0x1,
+    PIT_MODE_RATE_GENERATOR = 0x2,
+    PIT_MODES_SQUARE_WAVE_GENERATOR = 0x3,
+    PIT_MODES_SW_TRIGGERRED_STROBE = 0x4,
+    PIT_MODES_HW_TRIGGERRED_STROBE = 0x5,
+};
+
+static timer_callback callbacks[100];
+static int registered_callbacks = 0;
+
+void add_timer_callback(timer_callback tc) {
+    callbacks[registered_callbacks++] = tc;
+}
+
+static void timer_interrupt_handler(registers_t *r) {
+    for (int i = 0; i < registered_callbacks; ++i) {
+        callbacks[i]();
+    }
+}
+
+struct pit_command_t {
+    unsigned char bcd : 1;
+    unsigned char operating_mode : 3;
+    unsigned char access_mode : 2;
+    unsigned char select_channel : 2;
+} __attribute__((packed));
+
+static void dec_sleep_counter(void);
+
+void init_pit() {
+    struct pit_command_t cmd = {
+        .select_channel = PIT_SELECT_CHANNEL0,
+        .access_mode = PIT_ACCESS_MODE_LOHIBYTE,
+        .operating_mode = PIT_MODES_SQUARE_WAVE_GENERATOR,
+        .bcd = 0,
+    };
+    port_byte_out(0x43, *(unsigned char *)(&cmd));
+    port_byte_out(0x40, PIT_PROGRAM_REG & 0xff);
+    port_byte_out(0x40, (PIT_PROGRAM_REG & 0xff00) >> 8);
+
+    register_interrupt_handler(IRQ0, timer_interrupt_handler);
+    add_timer_callback(dec_sleep_counter);
+}
+
+static int sleep_counter = 0;
+
+static void dec_sleep_counter(void) {
+    sleep_counter--;
+}
+
+void msleep(int ms) {
+    sleep_counter = ms / 10;
+    while (sleep_counter > 0) {
+        asm("hlt");
+    }
+}
diff --git a/drivers/pit.h b/drivers/pit.h
new file mode 100644
index 0000000..01b72ad
--- /dev/null
+++ b/drivers/pit.h
@@ -0,0 +1,8 @@
+#pragma once
+
+typedef void (*timer_callback)(void);
+
+void init_pit(void);
+void add_timer_callback(timer_callback tc);
+
+void msleep(int ms);
diff --git a/kernel.c b/kernel.c
index db26e72..e502a2c 100644
--- a/kernel.c
+++ b/kernel.c
@@ -7,6 +7,7 @@ asm(".asciz \"kernel start\\n\"");
 #include "drivers/vga.h"
 #include "drivers/ata.h"
 #include "drivers/misc.h"
+#include "drivers/pit.h"
 #include "drivers/uart.h"
 #include "fs/fs.h"
 #include "lib/string.h"
@@ -16,6 +17,7 @@ asm(".asciz \"kernel start\\n\"");
 void _start() {
     load_gdt();
     init_keyboard();
+    init_pit();
     uartinit();
     load_idt();
     sti();
@@ -35,6 +37,11 @@ void _start() {
         if (kbd_buf_size > 0 && kbd_buf[kbd_buf_size-1] == '\n') {
             if (!strncmp("halt\n", kbd_buf, kbd_buf_size)) {
                 qemu_shutdown();
+            } else if (!strncmp("work\n", kbd_buf, kbd_buf_size)) {
+                for (int i = 0; i < 5; ++i) {
+                    msleep(1000);
+                    printk(".");
+                }
             } else if (!strncmp("run ", kbd_buf, 4)) {
                 kbd_buf[kbd_buf_size-1] = '\0';
                 const char* cmd = kbd_buf + 4;