From 2682bc5d1d864341aaeb42a449db73c3ecd16d70 Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Wed, 30 Dec 2020 19:07:31 +0000
Subject: Initial import

---
 src/ubox/ubox_isr.z80 | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 src/ubox/ubox_isr.z80

(limited to 'src/ubox/ubox_isr.z80')

diff --git a/src/ubox/ubox_isr.z80 b/src/ubox/ubox_isr.z80
new file mode 100644
index 0000000..cceb2c6
--- /dev/null
+++ b/src/ubox/ubox_isr.z80
@@ -0,0 +1,79 @@
+.globl _ubox_init_isr
+.globl _ubox_tick
+.globl ubox_isr_wait_ticks
+.globl ubox_isr_wait_tick
+.globl ubox_usr_isr
+.globl ___sdcc_call_hl
+
+HTIMI_HOOK = 0xfd9f
+
+SCNCNT = 0xf3f6
+REPCNT = 0xf3f7
+
+_ubox_init_isr::
+	di
+	ld a, l
+	ld (ubox_isr_wait_ticks), a
+	xor a
+	ld (ubox_isr_wait_tick), a
+	ld (_ubox_tick), a
+	ld (ubox_usr_isr), a
+	ld (ubox_usr_isr+1), a
+	ld hl, #ubox_isr
+	ex de, hl
+	ld hl, #HTIMI_HOOK
+	ld a, #0xc3
+	ld (hl), a
+	inc hl
+	ld (hl), e
+	inc hl
+	ld (hl), d
+	ei
+	ret
+
+ubox_isr:
+        push af
+	push ix
+	push iy
+	push bc
+	push hl
+	push de
+
+	; stop BIOS reading keyboard buffer
+	xor a
+	ld (SCNCNT), a
+	ld (REPCNT), a
+
+	ld hl, #ubox_isr_wait_tick
+	inc (hl)
+	inc hl
+	inc (hl)
+	inc hl
+	inc hl
+
+	; check user isr, only MSB
+	ld a, (hl)
+	or a
+	jr z, no_user_isr
+
+	dec hl
+	ld l, (hl)
+	ld h, a
+	call ___sdcc_call_hl
+
+no_user_isr:
+	pop de
+	pop hl
+	pop bc
+	pop iy
+	pop ix
+        pop af
+	ret
+
+.area _DATA
+
+ubox_isr_wait_ticks: .ds 1
+ubox_isr_wait_tick: .ds 1
+_ubox_tick: .ds 1
+
+ubox_usr_isr: .ds 2
-- 
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