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/*
RCC-Project
Copyright (C) 2026 Richard Qin
This file is part of RCC-Project.
*/
#include "bios.h"
#include "regs.h"
#define BIOS_CF 0x0001u
#define BIOS_INVALID_FUNCTION 0x86u
#define BDA_COM_PORTS 0x0400u
#define BDA_COM_TIMEOUTS 0x047Cu
#define BIOS_COM_PORT_COUNT 4u
void
int14_service (struct bios_regs *regs)
{
u8 function;
u8 status;
u8 value;
u8 timeout;
u16 port;
u16 base;
u16 result;
volatile u16 *ports;
volatile u8 *timeouts;
function = (u8)(regs->eax >> 8);
port = (u16)regs->edx;
ports = (volatile u16 *)BDA_COM_PORTS;
timeouts = (volatile u8 *)BDA_COM_TIMEOUTS;
/* BIOS numbers COM ports through DX and advertises their bases in BDA. */
if (function > 0x03u || port >= BIOS_COM_PORT_COUNT || ports[port] == 0u)
{
regs->eax
= (regs->eax & 0xFFFF00FFu) | ((u32)BIOS_INVALID_FUNCTION << 8);
regs->flags |= BIOS_CF;
return;
}
base = ports[port];
timeout = timeouts[port];
switch (function)
{
case 0x00u:
result = serial_configure (base, (u8)regs->eax);
regs->eax = (regs->eax & 0xFFFF0000u) | result;
break;
case 0x01u:
status = serial_transmit (base, (u8)regs->eax, timeout);
regs->eax = (regs->eax & 0xFFFF00FFu) | ((u32)status << 8);
break;
case 0x02u:
value = (u8)regs->eax;
status = serial_receive (base, &value, timeout);
regs->eax = (regs->eax & 0xFFFF0000u) | ((u32)status << 8) | value;
break;
case 0x03u:
result = serial_status (base);
regs->eax = (regs->eax & 0xFFFF0000u) | result;
break;
}
/* As in SeaBIOS, timeouts use AH bit 7; CF denotes an invalid call. */
regs->flags &= (u16)~BIOS_CF;
}
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