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