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46 lines
1.8 KiB
46 lines
1.8 KiB
21 July 1996
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The boot record is NOT executable. Any attempt to execute it will produce
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varied effects ranging from a HALT to only a single load or jump. The
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arguments of the instructions are simply intended to make addresses available
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to the ROM Boot loader. The layout is:
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ORG 8000H
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DB 76H ; HALT instruction
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LD HL,CCP-80H ; Base load point assuming 128 bytes for
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; this Boot Record size.
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RET ; (safety)
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JP BIOS ; This address is for the CBOOT entry in the
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; relocated System image. Execution should
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; commence at the argument of this jump.
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Accessing the relevant parameters from the ROM, then, normally consists of
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getting the Load Address from 8002H, and the BIOS CBOOT Entry point from
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8006H. It is recommended that the jump itself not be executed, but use a
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vectored approach such as the sequence:
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LD HL,(8006H)
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JP (HL)
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The remainder of this record is available for transferring parameters to the
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Bios as part of the CBOOT setup. Parameters may be addressed by absolute
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values such as 8020H, etc.
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Since the two location addresses are variable depending on the system size
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generated, a checksum of the boot record is not feasible without generating
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an entirely new, unique utility. That defeats the intent of this effort which
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is to retain a common suite of utilities across multiple platforms. Validation
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of the Boot record instead can check the absolute bytes at any or all of the
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following locations:
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8000 - 76H
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8001 - 21H
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8004 - 0C9H
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8005 - 0C3H
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Another possibility which may be implemented is to embed an ASCII Text string
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in the available space. This may be a visual thing, but there comes a limit
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to complexity vs reliability.
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Hal
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