mirror of https://github.com/mgcaret/of816.git
86 lines
3.4 KiB
Markdown
86 lines
3.4 KiB
Markdown
# W65C816SXB
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This is a port to WDC's [W65C816SXB](https://wdc65xx.com/boards/w65c816sxb-engineering-development-system/)
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development board. To build it, change to the platform directory and run
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build.sh. This will output a binary named "forth" that is suitable for placing
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in one of the Flash ROM banks of the W65C816SXB at $8000. Andrew Jacob's
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[w65c816sxb-hacker](https://github.com/andrew-jacobs/w65c816sxb-hacker) is
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suitable for this. Note that OF816 currently uses the USB port as the console
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device.
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You may also create a completely custom ROM image that replaces the WDC monitor
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with OF816, all that is required (assuming you are not going to use interrupts)
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is to point the RESET vector to $8000. It may be desirable to point the NMI
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vector at a routine that resets the system stack pointer and jumps to
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``_Forth_ui``.
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While this platform provides the "reference" platform with regards to system
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implementation, configuring it and making it work are an advanced topic.
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**Note:** None of WDC's tools are used to build OF816.
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## Port Features
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### Banked ROM Access
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The platform words include ``$SXB-READROM`` ( rom_addr dest_addr size -- ).
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This word allows copying size bytes from any bank in the ROM into dest_addr.
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The rom_addr is an address of the form $bb00xxxx where bb is the bank number
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(0-3) and xxxx is the physical address of the memory in bank 0. I.e. the
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valid ranges are $00008000-$0000FFFF, $01008000-$0100FFFF, etc.
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### FCode/romfs ROM Loader
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If FCode support is enabled, the word ``$SXB-ROMLDR`` is included in the
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platform words. This encapsulates ``fcode/romloader.fs`` and executing it will
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cause the ROM Loader and romfs words to be installed (romfs support may be
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disabled, see the source).
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The ROM Loader keeps a $100-byte cache of the last ROM page read in order to
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reduce the number of bank-switch/copy operations.
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Once the ROM Loader and romfs are installed, the following words are available:
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#### FCode Loader Words
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``$SXB-ROM-FCODE-AT?`` ( rom-addr -- f ) f is true if there is a FCode magic
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("MGFC") at the given ROM address. rom-addr must be on a page boundary.
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``$SXB-ROM-BYTE-LOAD`` ( rom-addr -- ) evaluate FCode at rom-addr, satisified
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by the conditions of ``$SXB-ROM-FCODE-AT?``.
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``$SXB-FC-BOOT`` ( -- ) search ROM at $1000-byte alignments for FCode identified
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by ``$SXB-ROM-FCODE-AT?`` and evaluate it.
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#### romfs Words
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romfs words generally follow the ANS Forth File Access word set guidelines,
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however they automatically throw non-zero IORs, therefore if the word returns
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normally the IOR is always 0. Consult the ANS standard for complete description
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of stack items.
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``INCLUDE`` ( <>"name" -- ... ) parse name and perform the function of INCLUDED.
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``INCLUDED`` ( c-addr u -- ... ) evaluate romfs file named by c-addr u.
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``OPEN-FILE`` ( c-addr u fam -- fileid 0 ) open romfs file, fam is discarded,
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access is always read-only.
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``READ-LINE`` ( c-addr u fileid - u2 f 0 ) read a line up to u bytes from file.
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``READ-FILE`` ( c-addr u fileid - u2 0 ) read up to u bytes from file.
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``FILE-POSITION`` ( fid -- u ) return read position in file
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``CLOSE-FILE`` ( fileid -- 0 ) close romfs file
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``ROMFS-LIST`` ( -- ) list files in romfs.
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``$SXB-ROM-ROMFS-AT?`` ( rom-addr -- f ) f is true if there is a ROMFS magic
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("MGFS") at the given ROM address. rom-addr must be on a page boundary.
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``$SXB-ROMFS`` ( -- u ) VALUE, zero if no romfs was found, otherwise contains
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the ROM address of the romfs.
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