[nostalgia/core/gba] Implement ISR

2020-07-09 23:32:34 -05:00
parent 4f79310084
commit 22a07afa9e
4 changed files with 139 additions and 6 deletions
@@ -0,0 +1,118 @@
+//
+// Copyright 2016 - 2020 gtalent2@gmail.com
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+
+.section .iwram, "ax", %progbits
+.arm
+.align
+
+.extern nostalgia_core_isr_vblank
+.extern nostalgia_core_isr_timer0
+.extern nostalgia_core_isr_timer1
+.extern nostalgia_core_isr_timer2
+.extern nostalgia_core_isr_timer3
+
+.equ REG_IFBIOS,         0x03fffff8
+
+.equ REG_IE,             0x04000200
+.equ REG_IF,             0x04000202
+.equ REG_IME,            0x04000208
+
+.equ Int_vblank,                  1
+.equ Int_hblank,                  2
+.equ Int_vcount,                  4
+.equ Int_timer0,                  8
+.equ Int_timer1,                 16
+.equ Int_timer2,                 32
+.equ Int_timer3,                 64
+.equ Int_serial,                128 // link cable
+.equ Int_dma0,                  256
+.equ Int_dma1,                  512
+.equ Int_dma2,                 1024
+.equ Int_dma3,                 2048
+.equ Int_dma4,                 4096
+.equ Int_dma5,                 8192
+.equ Int_input,               16384 // gamepad
+.equ Int_cart,                32768 // cartridge removed
+
+
+.global isr
+.type isr, %function
+isr:
+	// read IE
+	ldr r0, =#REG_IE
+	ldrh r1, [r0] // r1 becomes IE value
+	ldrh r2, [r0, #2] // r2 becomes IF value
+	and r1, r1, r2 // r1 becomes IE & IF
+	// done with r2 as IF value
+
+	// Acknowledge IRQ in REG_IF
+	strh r1, [r0, #2]
+	ldr r0, =#REG_IFBIOS
+	// Acknowledge IRQ in REG_IFBIOS
+	ldrh r2, [r0] // r2 becomes REG_IFBIOS value
+	orr r2, r2, r1
+	strh r2, [r0]
+	// done with r2 as IFBIOS value
+	// done with r0 as REG_IE
+
+	// clear IME to disable interrupts
+	ldr r2, =#REG_IME
+	mov r0, #0
+	str r0, [r2]
+
+	// enter system mode
+	mrs r0, cpsr
+	bic r0, r0, #0xDF
+	orr r0, r0, #0x1F
+	msr cpsr, r0
+
+	push {lr}
+	ldr lr, =isr_end
+
+	////////////////////////////////////////////////////
+	// Interrupt Table Begin                          //
+	////////////////////////////////////////////////////
+
+	cmp r1, #Int_vblank
+	beq nostalgia_core_isr_vblank
+
+	cmp r1, #Int_timer0
+	beq nostalgia_core_isr_timer0
+
+	cmp r1, #Int_timer1
+	beq nostalgia_core_isr_timer1
+
+	cmp r1, #Int_timer2
+	beq nostalgia_core_isr_timer2
+
+	cmp r1, #Int_timer3
+	beq nostalgia_core_isr_timer3
+
+	////////////////////////////////////////////////////
+	// Interrupt Table End                            //
+	////////////////////////////////////////////////////
+
+
+isr_end:
+	// restore lr from before the Interrupt Table
+	pop {lr}
+
+	// re-enter irq mode
+	mrs r0, cpsr
+	bic r0, r0, #0xDF
+	orr r0, r0, #0x92
+	msr cpsr, r0
+
+	// set IME to re-enable interrupts
+	ldr r2, =#REG_IME
+	mov r0, #1
+	str r0, [r2]
+
+	bx lr
+
+// vim: ft=armv4