Subversion Repositories s80186

// Copyright Jamie Iles, 2017

//

// This file is part of s80x86.

//

// s80x86 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.

//

// s80x86 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 s80x86.  If not, see .

.code16

.section .reset.text, "ax"

.globl _reset

_reset:

    ljmp $0xf000, $_start

.section .model, "a"

    .byte 0xff

    .byte 0x00

.section .entry.text, "ax"

.globl _start

_start:

    // Wait for SDRAM to initialize

    mov $0xfffc, %dx

    mov $1, %ax

1:

    in (%dx), %ax

    cmp $0x1, %ax

    jne 1b

    mov %cs, %ax

    mov %ax, %ss

    mov %ax, %ds

    mov %ax, %es

    // Clear bss

    mov $bss_start, %di

    mov $bss_end, %cx

    sub $bss_start, %cx

    mov $0, %al

    rep stosb

    // Initialize rw data

    mov $data_start, %di

    mov $data_end, %cx

    sub $data_start, %cx

    mov $_data_load, %si

    rep movsb

    movw $stack_start, %sp

    jmp root

.section .data

bios_ss:

    .word 0xf000

bios_sp:

    .word stack_start

.section .bss

saved_ss:

    .word 0

saved_sp:

    .word 0

.section .text, "ax"

.globl irq_entry

irq_entry:

    // Save current stack pointer, load BIOS stack

    mov %ss, %cs:saved_ss

    mov %sp, %cs:saved_sp

    mov %cs:bios_ss, %ss

    mov %cs:bios_sp, %sp

    // Save registers, setup stack frame

    push %ds

    pusha

    mov %sp, %bp

    push %bp

    // Load flags from iret frame, store in callregs

    mov %cs:saved_ss, %ds

    mov %cs:saved_sp, %bx

    mov 0(%bx), %ax

    mov 6(%bx), %bx

    mov %bx, 18(%bp)

    // Use SS as DS inside the BIOS for stack-local variables that are passed

    // by address

    mov %ss, %bp

    mov %bp, %ds

    call *%ax

    // Discard regs pointer parameter

    add $2, %sp

    mov %sp, %bp

    // Write possibly updated flags to the iret frame

    mov 18(%bp), %ax

    mov %cs:saved_ss, %ds

    mov %cs:saved_sp, %bx

    mov %ax, 6(%bx)

    // Restore all regs apart from flags - the iret frame has been updated

    // already

    popa

    pop %ds

    // Restore the callers stack

    mov %cs:saved_ss, %ss

    mov %cs:saved_sp, %sp

    add $2, %sp

    iret

.macro int_handler vector, function

.pushsection .rodata.vectors

    .align 4

    .word \vector

    .word \function

.popsection

.endm

stub_irq:

    iret

int_handler 0x1c, stub_irq

timer_irq:

    cli

    push %ds

    push %bx

    push %ax

    push %dx

    movw $0x40, %bx

    mov %bx, %ds

    movw $0x6c, %bx

    add $1, %ds:0(%bx)

    adc $0, %ds:2(%bx)

    int $0x1c

    movb $0x20, %al

    outb %al, $0x20

    pop %dx

    pop %ax

    pop %bx

    pop %ds

    iret

int_handler 0x08, timer_irq

.pushsection ".bios_date", "a"

    .ascii BIOS_BUILD_DATE

.popsection