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/*
RCC-Project
Copyright (C) 2026 Richard Qin
This file is part of RCC-Project.
RCC-Project 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.
RCC-Project 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
RCC-Project; see the file COPYING. If not see
<http://www.gnu.org/licenses/>.
*/
#include "bios.h"
#include "io.h"
#define COM1_BASE 0x03F8u
#define COM_DATA_OFFSET 0x00u
#define COM_IER_OFFSET 0x01u
#define COM_FCR_OFFSET 0x02u
#define COM_LCR_OFFSET 0x03u
#define COM_MCR_OFFSET 0x04u
#define COM_LSR_OFFSET 0x05u
#define COM_MSR_OFFSET 0x06u
#define COM_LCR_DLAB 0x80u
#define COM_LCR_8N1 0x03u
#define COM_FCR_ENABLE_FIFO 0x01u
#define COM_FCR_CLEAR_RX 0x02u
#define COM_FCR_CLEAR_TX 0x04u
#define COM_FCR_TRIGGER_14 0xC0u
#define COM_MCR_DTR 0x01u
#define COM_MCR_RTS 0x02u
#define COM_MCR_OUT2 0x08u
#define COM_LSR_THRE 0x20u
#define COM_LSR_IDLE 0x40u
#define COM_LSR_DATA_READY 0x01u
#define BIOS_SERIAL_TIMEOUT 0x80u
#define PIT_COUNTER0 0x0040u
#define PIT_COMMAND 0x0043u
static u16
com1_port (u16 offset)
{
return (u16)(COM1_BASE + offset);
}
/* Latching channel 0 works while the protected-mode service has IRQs off. */
u16
serial_timer_counter (void)
{
u16 counter;
io_out8 (PIT_COMMAND, 0x00u);
counter = io_in8 (PIT_COUNTER0);
counter |= (u16)((u16)io_in8 (PIT_COUNTER0) << 8);
return counter;
}
static int
serial_wait (u16 base, u8 mask, u8 timeout, u8 *status)
{
u16 previous;
u16 current;
u32 elapsed;
u32 duration;
previous = serial_timer_counter ();
elapsed = 0;
/* One BDA timeout unit is one 65536-clock BIOS timer tick. */
duration = (u32)timeout << 16;
for (;;)
{
*status = io_in8 ((u16)(base + COM_LSR_OFFSET));
if ((*status & mask) == mask)
return 1;
if (elapsed >= duration)
{
*status |= BIOS_SERIAL_TIMEOUT;
return 0;
}
current = serial_timer_counter ();
elapsed += (u16)(previous - current);
previous = current;
}
}
u16
serial_status (u16 base)
{
u8 line;
u8 modem;
line = io_in8 ((u16)(base + COM_LSR_OFFSET));
modem = io_in8 ((u16)(base + COM_MSR_OFFSET));
return (u16)(((u16)line << 8) | modem);
}
u16
serial_configure (u16 base, u8 parameters)
{
static const u16 divisors[]
= { 1047u, 768u, 384u, 192u, 96u, 48u, 24u, 12u };
u16 divisor;
/* INT 14h AL: bits 7:5 select baud; bits 4:0 are the UART format. */
divisor = divisors[parameters >> 5];
io_out8 ((u16)(base + COM_LCR_OFFSET), COM_LCR_DLAB);
io_out8 ((u16)(base + COM_DATA_OFFSET), (u8)divisor);
io_out8 ((u16)(base + COM_IER_OFFSET), (u8)(divisor >> 8));
io_out8 ((u16)(base + COM_LCR_OFFSET), parameters & 0x1Fu);
/* Do not reset the FIFO here: pending terminal input must survive. */
return serial_status (base);
}
u8
serial_transmit (u16 base, u8 value, u8 timeout)
{
u8 status;
if (serial_wait (base, COM_LSR_THRE | COM_LSR_IDLE, timeout, &status))
io_out8 ((u16)(base + COM_DATA_OFFSET), value);
return status;
}
u8
serial_receive (u16 base, u8 *value, u8 timeout)
{
u8 status;
if (serial_wait (base, COM_LSR_DATA_READY, timeout, &status))
*value = io_in8 ((u16)(base + COM_DATA_OFFSET));
return status;
}
int
serial_try_receive (u16 base, u8 *value)
{
u8 status;
status = io_in8 ((u16)(base + COM_LSR_OFFSET));
if ((status & COM_LSR_DATA_READY) == 0u)
return 0;
*value = io_in8 ((u16)(base + COM_DATA_OFFSET));
return 1;
}
void
serial_init (void)
{
// clang-format off
io_out8(com1_port(COM_IER_OFFSET), 0x00u);
io_out8(com1_port(COM_LCR_OFFSET), COM_LCR_DLAB);
io_out8(com1_port(COM_DATA_OFFSET), 0x01u);
io_out8(com1_port(COM_IER_OFFSET), 0x00u);
io_out8(com1_port(COM_LCR_OFFSET), COM_LCR_8N1);
io_out8(
com1_port(COM_FCR_OFFSET),
COM_FCR_ENABLE_FIFO |
COM_FCR_CLEAR_RX |
COM_FCR_CLEAR_TX |
COM_FCR_TRIGGER_14
);
io_out8(
com1_port(COM_MCR_OFFSET),
COM_MCR_DTR |
COM_MCR_RTS |
COM_MCR_OUT2
);
// clang-format on
}
void
serial_putc (u8 value)
{
while ((io_in8 (com1_port (COM_LSR_OFFSET)) & COM_LSR_THRE) == 0u)
{
}
io_out8 (com1_port (COM_DATA_OFFSET), value);
}
void
serial_write (const char *text)
{
while (*text != '\0')
{
serial_putc ((u8)*text);
++text;
}
}
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