From edf9e71e2a7b6b89775c29cf28c19c6b89992c25 Mon Sep 17 00:00:00 2001
From: aqua <aqua@iserlohn-fortress.net>
Date: Mon, 28 Mar 2022 20:03:38 +0300
Subject: Initial commit

x86 kernel that prints a hello world message to com1
---
 devices/uart_16550.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 devices/uart_16550.c

(limited to 'devices/uart_16550.c')

diff --git a/devices/uart_16550.c b/devices/uart_16550.c
new file mode 100644
index 0000000..7cec968
--- /dev/null
+++ b/devices/uart_16550.c
@@ -0,0 +1,68 @@
+#include "uart_16550.h"
+#include <sys/io.h>
+
+int
+uart_init(enum UART port)
+{
+  outb(0x00, port + 1); // Disable all interrupts
+  outb(0x80, port + 3); // Enable DLAB (set baud rate divisor)
+  outb(0x03, port + 0); // Set divisor to 3 (lo byte) 38400 baud
+  outb(0x00, port + 1); //                  (hi byte)
+  outb(0x03, port + 3); // 8 bits, no parity, one stop bit
+  outb(0xc7, port + 2); // Enable FIFO, clear them, with 14-byte threshold
+  outb(0x0b, port + 4); // IRQs enabled, RTS/DSR set
+  outb(0x1e, port + 4); // Set in loopback mode, test the serial chip
+  outb(0xae, port + 0); // Test serial chip (send byte 0xAE and check if serial
+                        // returns same byte)
+
+  // Check if serial is faulty (i.e: not same byte as sent)
+  if (inb(port + 0) != 0xae) {
+    return 1;
+  }
+
+  // If serial is not faulty set it in normal operation mode
+  // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
+  outb(0x0f, port + 4);
+  return 0;
+}
+
+int
+uart_thre(enum UART port)
+{
+  return inb(port + LineStatus) & THRE;
+}
+
+void
+uart_write(enum UART port, char a)
+{
+  while (uart_thre(port) == 0)
+    ;
+  outb(a, port);
+
+  if (a == '\n') {
+    while (uart_thre(port) == 0)
+      ;
+    outb('\r', port);
+  }
+}
+
+int
+uart_puts(enum UART port, const char *string, int length)
+{
+  int written = 0;
+
+  if (length == -1)
+    while (*string != '\0') {
+      uart_write(port, *string);
+      ++string;
+      ++written;
+    }
+
+  else
+    for (int i = 0; i < length; ++i) {
+      uart_write(port, string[i]);
+      ++written;
+    }
+
+  return written;
+}
-- 
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