--- /dev/null
+; pcboot - bootable PC demo/game kernel
+; Copyright (C) 2018-2023 John Tsiombikas <nuclear@member.fsf.org>
+;
+; 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 <https://www.gnu.org/licenses/>.
+
+ section .data
+ align 4
+ dw 0
+idtr_desc:
+lim: dw 0
+addr: dd 0
+
+ section .text
+; void set_idt(uint32_t addr, uint16_t limit)
+ global set_idt
+set_idt:
+ mov eax, [esp + 4]
+ mov [addr], eax
+ mov ax, [esp + 8]
+ mov [lim], ax
+ lidt [idtr_desc]
+ ret
+
+; int get_intr_flag()
+ global get_intr_flag
+get_intr_flag:
+ pushf
+ pop eax
+ ; bit 9 of eflags is IF
+ shr eax, 9
+ and eax, 1
+ ret
+
+; void set_intr_flag(int onoff)
+ global set_intr_flag
+set_intr_flag:
+ cmp dword [esp + 4], 0
+ jz .off
+ sti
+ ret
+.off: cli
+ ret
+
+; interrupt entry with error code macro
+; this macro generates an interrupt entry point for the
+; exceptions which include error codes in the stack frame
+%macro ientry_err 2
+ global intr_entry_%2
+intr_entry_%2:
+ push dword %1
+ jmp intr_entry_common
+%endmacro
+
+; interrupt entry without error code macro
+; this macro generates an interrupt entry point for the interrupts
+; and exceptions which do not include error codes in the stack frame
+; it pushes a dummy error code (0), to make the stack frame identical
+%macro ientry_noerr 2
+ global intr_entry_%2
+intr_entry_%2:
+ push dword 0
+ push dword %1
+ jmp intr_entry_common
+%endmacro
+
+; common code used by all entry points. calls dispatch_intr()
+; defined in intr.c
+ extern dispatch_intr
+intr_entry_common:
+ ; save general purpose registers
+ pusha
+ call dispatch_intr
+intr_ret_local:
+ ; restore general purpose registers
+ popa
+ ; remove error code and intr num from stack
+ add esp, 8
+ iret
+
+; special case for the timer interrupt, to avoid all the overhead of
+; going through the C interrupt dispatcher 250 times each second
+; extern nticks
+; global intr_entry_fast_timer
+;intr_entry_fast_timer:
+; inc dword [nticks]
+; ; signal end of interrupt
+; push eax
+; mov al, 20h
+; out 20h, al
+; pop eax
+; iret
+
+; special case for IRQ 7 and IRQ 15, to catch spurious interrupts
+PIC1_CMD equ 0x20
+PIC2_CMD equ 0xa0
+OCW2_EOI equ 0x20
+OCW3_ISR equ 0x0b
+
+ global irq7_entry_check_spurious
+irq7_entry_check_spurious:
+ push eax
+ mov al, OCW3_ISR
+ out PIC1_CMD, al
+ in al, PIC1_CMD
+ and al, 80h
+ pop eax
+ jnz intr_entry_irq7
+ iret
+
+ global irq15_entry_check_spurious
+irq15_entry_check_spurious:
+ push eax
+ mov al, OCW3_ISR
+ out PIC2_CMD, al
+ in al, PIC2_CMD
+ and al, 80h
+ jnz .legit
+ ; it was spurious, send EOI to master PIC and iret
+ mov al, OCW2_EOI
+ out PIC1_CMD, al
+ pop eax
+ iret
+.legit: pop eax
+ jmp intr_entry_irq15
+
+
+; XXX not necessary for now, just leaving it in in case it's useful
+; down the road.
+;
+; intr_ret is called by context_switch to return from the kernel
+; to userspace. The argument is a properly formed intr_frame
+; structure with the saved context of the new task.
+;
+; First thing to do is remove the return address pointing back
+; to context_switch, which then leaves us with a proper interrupt
+; stack frame, so we can jump right in the middle of the regular
+; interrupt return code above.
+ global intr_ret
+intr_ret:
+ add esp, $4
+ jmp intr_ret_local
+
+; by including interrupts.h with ASM defined, the macros above
+; are expanded to generate all required interrupt entry points
+%define INTR_ENTRY_EC(n, name) ientry_err n, name
+%define INTR_ENTRY_NOEC(n, name) ientry_noerr n, name
+
+%include 'intrtab.h'
+
+; vi:set ts=8 sts=8 sw=8 ft=nasm:
projects / com32 / blobdiff