From 8f65a42f4f046442d50e7ceaa05689d786ea59c2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Valt=C3=BDr=20=C3=96rn=20Kjartansson?= <valtyr@gmail.com>
Date: Sat, 26 Jun 2021 17:00:33 +0000
Subject: [PATCH] Add basic PIT implementation

---
 src/impl/kernel/main.c |  9 +++++-
 src/impl/kernel/pit.c  | 66 ++++++++++++++++++++++++++++++++++++++++++
 src/intf/pit.h         | 39 +++++++++++++++++++++++++
 3 files changed, 113 insertions(+), 1 deletion(-)
 create mode 100644 src/impl/kernel/pit.c
 create mode 100644 src/intf/pit.h

diff --git a/src/impl/kernel/main.c b/src/impl/kernel/main.c
index 7be0660..e87b85f 100644
--- a/src/impl/kernel/main.c
+++ b/src/impl/kernel/main.c
@@ -4,6 +4,7 @@
 #include "dt.h"
 #include "ps2.h"
 #include "rtc.h"
+#include "pit.h"
 #include "sb16.h"
 
 MultibootInfo systemInfo;
@@ -13,6 +14,9 @@ extern FBImage popcorn_logo;
 extern u16 popcorn_chime[];
 extern u32 popcorn_chime_length;
 
+static u8 s_pit_counter = 0;
+static u8 s_swap_counter = 0;
+
 void kernel_main(u32 magic, void *addr)
 {
     BIOSGreeting();
@@ -27,6 +31,7 @@ void kernel_main(u32 magic, void *addr)
     InitDescriptorTables();
 
     RTCInit();
+    PITInit();
 
     // Initialize framebuffer and display greeting
     FBInit(systemInfo.framebufferWidth, systemInfo.framebufferHeight, (void *)systemInfo.framebufferAddress);
@@ -34,10 +39,12 @@ void kernel_main(u32 magic, void *addr)
     FBBlit(systemInfo.framebufferWidth / 2 - popcorn_logo.width / 2, systemInfo.framebufferHeight / 2 - popcorn_logo.height / 2, &popcorn_logo);
     FBOutput();
 
+    // As of right now this shuts down the emulator
+    // when ESC is pressed.
     PS2Init();
 
     SB16Init();
-    SB16DirectPlay(popcorn_chime, popcorn_chime_length);
+    // SB16DirectPlay(popcorn_chime, popcorn_chime_length);
 
     while (true)
     {
diff --git a/src/impl/kernel/pit.c b/src/impl/kernel/pit.c
new file mode 100644
index 0000000..985ad0f
--- /dev/null
+++ b/src/impl/kernel/pit.c
@@ -0,0 +1,66 @@
+#include "pit.h"
+
+static ISRHandler s_pit_handler = NULL;
+
+void __pit_handler(registers_t reg)
+{
+    if (s_pit_handler != NULL)
+        s_pit_handler(reg);
+}
+
+void __pit_cmd_tx(u8 cmd)
+{
+    outb(PIT_REG_COMMAND, cmd);
+}
+
+void __pit_data_tx(u8 data, u8 counter)
+{
+    u8 port = (counter == PIT_OCW_COUNTER_0) ? PIT_REG_COUNTER0 : ((counter == PIT_OCW_COUNTER_1) ? PIT_REG_COUNTER1 : PIT_REG_COUNTER2);
+    outb(port, data);
+}
+
+void __pit_start_counter(u32 freq, u8 counter, u8 mode)
+{
+    if (freq == 0)
+        return;
+
+    BIOSPrintf("PIT counter %d stared with frequency %dHz\n", counter / 0x40, freq);
+
+    uint16_t divisor = (uint16_t)(1193181 / (uint16_t)freq);
+
+    // send operational command words
+    uint8_t ocw = 0;
+    ocw = (ocw & ~PIT_OCW_MASK_MODE) | mode;
+    ocw = (ocw & ~PIT_OCW_MASK_RL) | PIT_OCW_RL_DATA;
+    ocw = (ocw & ~PIT_OCW_MASK_COUNTER) | counter;
+    __pit_cmd_tx(ocw);
+
+    // set frequency rate
+    __pit_data_tx(divisor & 0xff, 0);
+    __pit_data_tx((divisor >> 8) & 0xff, 0);
+}
+
+void PITInit()
+{
+    BIOSPrintf("Initializing PIT...\n");
+
+    ISRRegisterHandler(IRQ_0, __pit_handler);
+
+    __pit_start_counter(60, PIT_OCW_COUNTER_0, PIT_OCW_MODE_SQUAREWAVEGEN);
+
+    BIOSPrintf("PIT initialized\n");
+}
+
+void PITAttach(ISRHandler handler)
+{
+    if (s_pit_handler != NULL)
+    {
+        BIOSPrint("Warning: PIT handler overwritten\n");
+    }
+    s_pit_handler = handler;
+}
+
+void PITDetach()
+{
+    s_pit_handler = NULL;
+}
diff --git a/src/intf/pit.h b/src/intf/pit.h
new file mode 100644
index 0000000..16ee77c
--- /dev/null
+++ b/src/intf/pit.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include "io.h"
+#include "isr.h"
+
+// Defines borrowed from levos
+// https://github.com/levex/osdev/blob/master/include/pit.h
+
+#define PIT_REG_COUNTER0 0x40
+#define PIT_REG_COUNTER1 0x41
+#define PIT_REG_COUNTER2 0x42
+#define PIT_REG_COMMAND 0x43
+
+#define PIT_OCW_MASK_BINCOUNT 1   //00000001
+#define PIT_OCW_MASK_MODE 0xE     //00001110
+#define PIT_OCW_MASK_RL 0x30      //00110000
+#define PIT_OCW_MASK_COUNTER 0xC0 //11000000
+
+#define PIT_OCW_BINCOUNT_BINARY 0 //0
+#define PIT_OCW_BINCOUNT_BCD 1    //1
+
+#define PIT_OCW_MODE_TERMINALCOUNT 0   //0000
+#define PIT_OCW_MODE_ONESHOT 0x2       //0010
+#define PIT_OCW_MODE_RATEGEN 0x4       //0100
+#define PIT_OCW_MODE_SQUAREWAVEGEN 0x6 //0110
+#define PIT_OCW_MODE_SOFTWARETRIG 0x8  //1000
+#define PIT_OCW_MODE_HARDWARETRIG 0xA  //1010
+
+#define PIT_OCW_RL_LATCH 0      //000000
+#define PIT_OCW_RL_LSBONLY 0x10 //010000
+#define PIT_OCW_RL_MSBONLY 0x20 //100000
+#define PIT_OCW_RL_DATA 0x30    //110000
+
+#define PIT_OCW_COUNTER_0 0    //00000000
+#define PIT_OCW_COUNTER_1 0x40 //01000000
+#define PIT_OCW_COUNTER_2 0x80 //10000000
+
+void PITInit();
+void PITAttach(ISRHandler);
\ No newline at end of file