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lowram.s@ cc2c9e0

Last change on this file since cc2c9e0 was 84920eb, checked in by Thomas Lopatic <thomas@…>, 7 years ago
Fixed wrongly replaced multiplications.
Property mode set to `100644`
File size: 4.9 KB

Line
1	\| ------------------------------------------------------------------------------
2	\| lowram.s -- create a GEMDOS compatible basepage for the Buchla 700
3	\| Version 10 -- 1988-03-28 -- D.N. Lynx Crowe
4	\| ------------------------------------------------------------------------------
5	\| Provides a GEMDOS compatible basepage and calls start_ to
6	\| get things rolling for applications on the Buchla 700.
7
8	\| Also sets the stack pointer to the high end of RAM.
9
10	\| WARNING: This code ONLY works for programs loaded into RAM.
11	\| ------------------------------------------------------------------------------
12	\| We expect the following to be the relative layout of memory:
13
14	\| lowram load address (this chunk of code)
15	\| ...
16	\| p_lowtpa start of 'TPA' / basepage address
17	\| ...
18	\| start_ first module (starts 'text' area)
19	\| ...
20	\| ... -text-
21	\| ...
22	\| _etext end of 'text' area + 1
23	\| basedat start of 'data' area (will usually be _etext)
24	\| ...
25	\| ... -data-
26	\| ...
27	\| _edata end of 'data' area + 1
28	\| basebss start of 'bss' area (will usually be _edata)
29	\| ...
30	\| ... -BSS-
31	\| ...
32	\| _end end of actual 'bss' area + 1
33	\| ...
34	\| ... -heap-
35	\| ...
36	\| HI_RAM-0x400 end of pseudo 'bss' area (cleared by fsmain.s)
37	\| ...
38	\| ... -stack margin-
39	\| ...
40	\| HI_RAM end of RAM + 1, initial stack address
41	\| ------------------------------------------------------------------------------
42	\| The startup code in fsmain.s uses the bss length to know how much RAM
43	\| to clear. We give it HI_RAM-0x400-basebss, and put the stack at HI_RAM.
44	\| The startup code clears from p_bbase through p_bbase+p_blen-1, inclusive.
45	\| This keeps fsmain.s from wiping itself out when it zaps the bss area.
46
47	\| The startup code (start_) in fsmain.s is entered with the address of
48	\| the basepage passed as a long word parameter on the top of the stack.
49	\| ------------------------------------------------------------------------------
50	.text
51
52	.page
53
54	\| Globals defined here:
55
56	.xdef LOWRAM
57	.xdef _Lo_RAM
58	.xdef _Hi_RAM
59
60	.xdef basebss
61	.xdef basedat
62	.xdef p_lowtpa
63	.xdef p_env
64
65	.xdef _p_tlen
66	.xdef _p_dlen
67
68	\| Globals referred to here:
69
70	.xref start_ \| entry point in fsmain.s
71	.xref _panic \| entry point in fsmain.s
72
73	.xref _edata \| supplied by loader
74	.xref _etext \| supplied by loader
75
76	\| ------------------------------------------------------------------------------
77	\| Memory setup:
78	\| ------------
79	\| The equate for HI_RAM must be set to match the memory configuration used.
80
81	\| For a 512K system, _Hi_RAM = 0x080000
82	\| For a 1024K system, _Hi_RAM = 0x100000
83
84	_Hi_RAM = 0x100000 \| highest RAM address + 1
85
86	.page
87
88	\| LOWRAM -- Startup code for Buchla 700 application programs
89	\| ------ ------------------------------------------------
90	_Lo_RAM:
91	LOWRAM: lea basebss,a0 \| setup bss base
92	move.l a0,p_bbase \| ...
93	lea _Hi_RAM-0x400,a1 \| setup faked bss length
94	suba.l a0,a1 \| ...
95	move.l a1,p_blen \| ...
96
97	lea basedat,a0 \| setup data base
98	move.l a0,p_dbase \| ...
99	lea _edata,a1 \| setup data length
100	suba.l a0,a1 \| ...
101	move.l a1,p_dlen \| ...
102
103	lea start_,a0 \| setup text base
104	move.l a0,p_tbase \| ...
105	lea _etext,a1 \| setup text length
106	suba.l a0,a1 \| ...
107	move.l a1,p_tlen \| ...
108
109	lea _Hi_RAM,a7 \| setup stack pointer
110
111	lea p_lowtpa,a0 \| setup TPA base
112	move.l a0,p_lowtpa \| ...
113	move.l a7,p_hitpa \| setup high TPA
114
115	move.l #p_lowtpa,-(a7) \| Pass basepage address
116	jsr start_ \| Start things going
117	addq.l #4,a7 \| Clean up stack
118
119	move.l #pmsg,-(a7) \| OOPS: panic()
120	jsr _panic \| ... shouldn't ever return
121	addq.l #4,a7
122
123	hstop: stop #0x2000 \| "Die, sucker!"
124	bra hstop
125
126	.page
127
128	\| The mess below is the basepage. It defines the start of the pseudo 'TPA'.
129	\| This MUST live in the 'text' segment for things to work.
130
131	p_lowtpa: .dc.l 0 \| low address of TPA
132	p_hitpa: .dc.l 0 \| high address + 1 of TPA
133	p_tbase: .dc.l 0 \| low address of text segment
134	p_tlen: .dc.l 0 \| length of text segment
135	p_dbase: .dc.l 0 \| low address of data segment
136	p_dlen: .dc.l 0 \| length of data segment
137	p_bbase: .dc.l 0 \| low address of BSS segment
138	p_blen: .dc.l 0 \| length of BSS segment
139	p_dta: .dc.l 0 \| pointer to DTA
140	p_parent: .dc.l 0 \| pointet to parent basepage
141	.dc.l 0
142	p_env: .dc.l 0 \| pointer to environment string
143	.ds.l 20
144	p_cmdlin: .dc.b 0 \| command line tail image
145	.ds.b 127
146
147	current:
148	BPLEN = current-p_lowtpa \| MUST be 0x0100 (or we goofed)
149
150	_p_tlen = p_tlen \| text length for MIDAS-VII
151	_p_dlen = p_dlen \| data length for MIDAS-VII
152
153	\| ------------------------------------------------------------------------------
154	.data
155	\| ------------------------------------------------------------------------------
156	.even
157
158	basedat: .ascii "*** data ***" \| start of data
159
160	pmsg: .asciz "returned from start_()" \| panic() message
161
162	\| ------------------------------------------------------------------------------
163	.bss
164	\| ------------------------------------------------------------------------------
165	.even
166
167	basebss: .ds.l 1 \| start of BSS
168
169	.end

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