kernel: drivers: Implement serial driver.

It's a very primitive driver for outputting to serial console.

9 files changed, 170 insertions, 3 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1ac5b3..d07656d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,6 +14,7 @@ set(QEMU_SYSTEM_CMD qemu-system-i386)
 
 set(QEMU_ARGUMENTS
   -cdrom ${CMAKE_BINARY_DIR}/cmos.iso
+  -serial stdio
 )
 
 add_custom_target(iso
@@ -31,6 +32,7 @@ add_custom_target(run
   ${QEMU_ARGUMENTS}
 
   DEPENDS iso
+  USES_TERMINAL
 )
 
 add_custom_target(run-gdb
@@ -40,6 +42,7 @@ add_custom_target(run-gdb
   -S
 
   DEPENDS iso
+  USES_TERMINAL
 )
 
 add_custom_target(clean-custom
diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index 0478740..206b728 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -7,8 +7,10 @@ set(KERNEL_SRC
   kernel/kernel.c
   kernel/halt.c
   kernel/stack_smashing_protector.c
+  kernel/io/io.c
 
   drivers/vga_text_buffer/vga_text_buffer.c
+  drivers/serial/serial.c
 
   libk/strlen.c
   libk/printk.c
diff --git a/kernel/drivers/serial/serial.c b/kernel/drivers/serial/serial.c
new file mode 100644
index 0000000..49362de
--- /dev/null
+++ b/kernel/drivers/serial/serial.c
@@ -0,0 +1,70 @@
+/*
+ * CMOS
+ * Copyright (C) 2024 Raghuram Subramani <raghus2247@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libk/string.h>
+
+#include <kernel/io.h>
+
+#include <drivers/serial.h>
+
+void
+serial_initialize(void)
+{
+  outb(PORT + 1, 0x00); // Disable all interrupts
+  outb(PORT + 3, 0x80); // Enable DLAB (set baud rate divisor)
+  outb(PORT + 0, 0x03); // Set divisor to 3 (lo byte) 38400 baud
+  outb(PORT + 1, 0x00); //                  (hi byte)
+  outb(PORT + 3, 0x03); // 8 bits, no parity, one stop bit
+  outb(PORT + 2, 0xC7); // Enable FIFO, clear them, with 14-byte threshold
+  outb(PORT + 4, 0x0B); // IRQs enabled, RTS/DSR set
+  outb(PORT + 4, 0x1E); // Set in loopback mode, test the serial chip
+  outb(PORT + 0, 0xAE); // Test serial chip (send byte 0xAE and check if serial
+                        // returns same byte)
+
+  // TODO: 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(PORT + 4, 0x0F);
+}
+
+static int
+is_transmit_empty()
+{
+  return inb(PORT + 5) & 0x20;
+}
+
+void
+serial_write_char(char a)
+{
+  while (is_transmit_empty() == 0)
+    ;
+
+  outb(PORT, a);
+}
+
+void
+serial_write_string(char *string)
+{
+  size_t size = strlen(string);
+  for (size_t i = 0; i < size; i++)
+    serial_write_char(string[i]);
+}
diff --git a/kernel/drivers/vga_text_buffer/vga_text_buffer.c b/kernel/drivers/vga_text_buffer/vga_text_buffer.c
index 3a63ccb..d7aa235 100644
--- a/kernel/drivers/vga_text_buffer/vga_text_buffer.c
+++ b/kernel/drivers/vga_text_buffer/vga_text_buffer.c
@@ -89,9 +89,9 @@ vga_text_buffer_write_char(char c)
 }
 
 void
-vga_text_buffer_write_string(char *data)
+vga_text_buffer_write_string(char *string)
 {
-  size_t size = strlen(data);
+  size_t size = strlen(string);
   for (size_t i = 0; i < size; i++)
-    vga_text_buffer_write_char(data[i]);
+    vga_text_buffer_write_char(string[i]);
 }
diff --git a/kernel/include/drivers/serial.h b/kernel/include/drivers/serial.h
new file mode 100644
index 0000000..869500f
--- /dev/null
+++ b/kernel/include/drivers/serial.h
@@ -0,0 +1,28 @@
+/*
+ * CMOS
+ * Copyright (C) 2024 Raghuram Subramani <raghus2247@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __drivers_serial_h
+#define __drivers_serial_h
+
+#define PORT 0x3f8 // COM1
+
+void serial_initialize(void);
+void serial_write_char(char);
+void serial_write_string(char *);
+
+#endif
diff --git a/kernel/include/kernel/io.h b/kernel/include/kernel/io.h
new file mode 100644
index 0000000..99a8aec
--- /dev/null
+++ b/kernel/include/kernel/io.h
@@ -0,0 +1,27 @@
+/*
+ * CMOS
+ * Copyright (C) 2024 Raghuram Subramani <raghus2247@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __kernel_io_h
+#define __kernel_io_h
+
+#include <stdint.h>
+
+uint8_t inb(uint16_t port);
+void outb(uint16_t port, uint8_t val);
+
+#endif
diff --git a/kernel/kernel/io/io.c b/kernel/kernel/io/io.c
new file mode 100644
index 0000000..f8feb32
--- /dev/null
+++ b/kernel/kernel/io/io.c
@@ -0,0 +1,33 @@
+#include <stdint.h>
+
+#include <kernel/io.h>
+
+/* Sends a 8/16/32-bit value on a I/O location. Traditional names are outb,
+ * outw and outl respectively. The a modifier enforces val to be placed in the
+ * eax register before the asm command is issued and Nd allows for one-byte
+ * constant values to be assembled as constants, freeing the edx register for
+ * other cases. */
+
+void
+outb(uint16_t port, uint8_t val)
+{
+  __asm__ volatile("outb %b0, %w1" : : "a"(val), "Nd"(port) : "memory");
+
+  /* There's an outb %al, $imm8 encoding, for compile-time constant port
+   * numbers that fit in 8b. (N constraint). Wider immediate constants would be
+   * truncated at assemble-time (e.g. "i" constraint). The  outb  %al, %dx
+   * encoding is the only option for all other cases. %1 expands to %dx because
+   * port  is a uint16_t.  %w1 could be used if we had the port number a wider
+   * C type */
+}
+
+/* Receives a 8/16/32-bit value from an I/O location. Traditional names are
+ * inb, inw and inl respectively. */
+
+uint8_t
+inb(uint16_t port)
+{
+  uint8_t ret;
+  __asm__ volatile("inb %w1, %b0" : "=a"(ret) : "Nd"(port) : "memory");
+  return ret;
+}
diff --git a/kernel/kernel/kernel.c b/kernel/kernel/kernel.c
index 511f3c3..4da19c3 100644
--- a/kernel/kernel/kernel.c
+++ b/kernel/kernel/kernel.c
@@ -18,12 +18,14 @@
 
 #include <libk/io.h>
 
+#include <drivers/serial.h>
 #include <drivers/vga_text_buffer.h>
 
 void
 kernel_main(void)
 {
   vga_text_buffer_initialize();
+  serial_initialize();
 
   printk("kernel_main: Started\n");
 }
diff --git a/kernel/libk/printk.c b/kernel/libk/printk.c
index f3a5085..4983c50 100644
--- a/kernel/libk/printk.c
+++ b/kernel/libk/printk.c
@@ -16,6 +16,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <drivers/serial.h>
 #include <drivers/vga_text_buffer.h>
 
 #include <libk/io.h>
@@ -24,4 +25,5 @@ void
 printk(char *msg)
 {
   vga_text_buffer_write_string(msg);
+  serial_write_string(msg);
 }