source: buchla-68k/vlib/vbank.s@ f40a309

Last change on this file since f40a309 was f40a309, checked in by Thomas Lopatic <thomas@…>, 7 years ago

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1* ------------------------------------------------------------------------------
2* vbank.s -- VSDD bank switching control functions
3* Version 3 -- 1989-12-19 -- D.N. Lynx Crowe
4*
5* unsigned
6* vbank(b)
7* unsigned b;
8*
9* Set VSDD Data Segment bank to b.
10* Return old bank select value.
11*
12*
13* vfwait()
14*
15* Wait for a FRAMESTOP update to transpire.
16* ------------------------------------------------------------------------------
17 .xdef _vbank
18 .xdef _vfwait
19*
20 .xref _v_regs
21*
22 .text
23*
24B .equ 8
25*
26OLDB .equ d6
27NEWB .equ d7
28*
29VSDD_R5 .equ 10
30VSDD_R11 .equ 22
31*
32VT_BASE .equ 128 * word offset of VSDD Access Table
33*
34VT_1 .equ VT_BASE+300 * high time
35VT_2 .equ VT_BASE+2 * low time
36*
37 .page
38* ------------------------------------------------------------------------------
39* vbank(b) -- change VSDD Data Segment bank to b. Return old bank.
40* Assumes a 128K byte window, sets S15..S11 to zero.
41* ------------------------------------------------------------------------------
42*
43
44_vbank: link a6,#0 * link stack frames
45 movem.l d5-d7,-(sp) * preserve registers
46 move.w _v_regs+VSDD_R5,OLDB * get v_regs[5]
47 lsr.w #6,OLDB * extract BS bits
48 move.w OLDB,d0 * ...
49 andi.w #2,d0 * ...
50 move.w OLDB,d1 * ...
51 lsr.w #2,d1 * ...
52 andi.w #1,d1 * ...
53 or.w d1,d0 * ...
54 move.w d0,OLDB * ...
55 cmp.w B(a6),OLDB * see if they're what we want
56 bne L2 * jump if not
57*
58 move.w B(a6),d0 * setup to return b
59 bra L1
60*
61L2: move.w B(a6),NEWB * get bank bits from b
62 lsl.w #6,NEWB * shift bits from b into BS bits
63 move.w NEWB,d0 * ...
64 andi.w #128,d0 * ...
65 lsl.w #2,NEWB * ...
66 andi.w #256,NEWB * ...
67 or.w NEWB,d0 * ...
68 move.w d0,_v_regs+VSDD_R5 * set v_regs[5] with new BS bits
69*
70vw1b: cmp.w #VT_1,_v_regs+VSDD_R11 * wait for FRAMESTOP
71 bcc vw1b * ...
72*
73vw2b: cmp.w #VT_1,_v_regs+VSDD_R11 * ...
74 bcs vw2b * ...
75*
76vw3b: cmp.w #VT_1,_v_regs+VSDD_R11 * ...
77 bcc vw3b * ...
78*
79vw4b: cmp.w #VT_2,_v_regs+VSDD_R11 * ...
80 bcs vw4b * ...
81*
82 move.w OLDB,d0 * setup to return OLDB
83*
84L1: tst.l (sp)+ * fixup stack
85 movem.l (sp)+,OLDB-NEWB * restore registers
86 unlk a6 * unlink stack frames
87 rts * return to caller
88*
89 .page
90*
91* ------------------------------------------------------------------------------
92* vfwait() -- Wait for a FRAMESTOP update to transpire.
93* ------------------------------------------------------------------------------
94*
95_vfwait: link a6,#0 * link stack frames
96*
97vw1a: cmp.w #VT_1,_v_regs+VSDD_R11 * wait for FRAMESTOP
98 bcc vw1a * ...
99*
100vw2a: cmp.w #VT_1,_v_regs+VSDD_R11 * ...
101 bcs vw2a * ...
102*
103vw3a: cmp.w #VT_1,_v_regs+VSDD_R11 * ...
104 bcc vw3a * ...
105*
106vw4a: cmp.w #VT_2,_v_regs+VSDD_R11 * ...
107 bcs vw4a * ...
108*
109 unlk a6 * unlink stack frames
110 rts * return to caller
111*
112 .end
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