From 7a6cf86e4dd3094ed5aa41bf76d93c28c89e85e7 Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.xyz>
Date: Wed, 20 Jan 2021 21:31:23 -0600
Subject: i386: add serial port support

Add support for serial communication in the i386 architecture.

Signed-off-by: Danny Holman <dholman@gymli.xyz>
---
 arch/i386/make.config   |  1 +
 arch/i386/pic.h         | 16 ++++++++++++++++
 arch/i386/serial.c      | 40 ++++++++++++++++++++++++++++++++++++++++
 include/kernel/serial.h |  8 ++++++++
 kernel/init.c           |  3 ++-
 5 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 arch/i386/pic.h
 create mode 100644 arch/i386/serial.c
 create mode 100644 include/kernel/serial.h

diff --git a/arch/i386/make.config b/arch/i386/make.config
index a5049af..680760f 100644
--- a/arch/i386/make.config
+++ b/arch/i386/make.config
@@ -4,3 +4,4 @@ KERNEL_ARCH_LIBS=
 
 KERNEL_ARCH_OBJS=$(ARCHDIR)/boot.o \
                  $(ARCHDIR)/tty.o \
+                 $(ARCHDIR)/serial.o \
diff --git a/arch/i386/pic.h b/arch/i386/pic.h
new file mode 100644
index 0000000..da4a2ee
--- /dev/null
+++ b/arch/i386/pic.h
@@ -0,0 +1,16 @@
+#ifndef PIC_H
+#define PIC_H
+
+#include <stdint.h>
+
+static inline void outb(uint16_t port, uint8_t value) {
+        asm volatile("outb %0, %1" : : "a"(value), "Nd"(port));
+}
+
+static inline uint8_t inb(uint16_t port) {
+        uint8_t ret;
+        asm volatile("inb %1, %0" : "=a"(ret) : "Nd"(port));
+        return ret;
+}
+
+#endif
diff --git a/arch/i386/serial.c b/arch/i386/serial.c
new file mode 100644
index 0000000..b172e82
--- /dev/null
+++ b/arch/i386/serial.c
@@ -0,0 +1,40 @@
+#include <kernel/serial.h>
+#include "pic.h"
+
+#define PORT 0x3f8
+
+static int serial_init(void) {
+        outb(PORT + 1, 0x00);
+        outb(PORT + 3, 0x80);
+        outb(PORT + 0, 0x03);
+        outb(PORT + 1, 0x00);
+        outb(PORT + 3, 0x03);
+        outb(PORT + 2, 0xC7);
+        outb(PORT + 4, 0x0B);
+        outb(PORT + 4, 0x1E);
+        outb(PORT + 0, 0xAE);
+
+        if (inb(PORT + 0) != 0xAE)
+                return -1;
+
+        outb(PORT + 4, 0x0F);
+        return 0;
+}
+
+int serial_recieved(void) {
+        return inb(PORT + 5) & 1;
+}
+
+char read_serial(void) {
+        while (serial_recieved() == 0);
+        return inb(PORT);
+}
+
+int is_transmit_empty(void) {
+        return inb(PORT + 5) & 0x20;
+}
+
+void write_serial(char a) {
+        while (is_transmit_empty() == 0);
+        outb(PORT, a);
+}
diff --git a/include/kernel/serial.h b/include/kernel/serial.h
new file mode 100644
index 0000000..a3a54b0
--- /dev/null
+++ b/include/kernel/serial.h
@@ -0,0 +1,8 @@
+#ifndef SERIAL_H
+#define SERIAL_H
+
+static int serial_init(void);
+char read_serial(void);
+void write_serial(char a);
+
+#endif
diff --git a/kernel/init.c b/kernel/init.c
index 576b7f4..ed6d1a7 100644
--- a/kernel/init.c
+++ b/kernel/init.c
@@ -3,5 +3,6 @@
 
 void kernel_main(void) {
         tty_init();
-        printf("Hello world %x", 100);
+        serial_init();
+        printf("Hello world\n");
 }
-- 
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