mirror of
https://github.com/mgcaret/of816.git
synced 2025-01-02 12:31:08 +00:00
86 lines
3.4 KiB
Markdown
86 lines
3.4 KiB
Markdown
|
# W65C816SXB
|
||
|
|
|
||
|
|
This is a port to WDC's [W65C816SXB](https://wdc65xx.com/boards/w65c816sxb-engineering-development-system/)
|
||
|
|
development board. To build it, change to the platform directory and run
|
||
|
|
build.sh. This will output a binary named "forth" that is suitable for placing
|
||
|
|
in one of the Flash ROM banks of the W65C816SXB at $8000. Andrew Jacob's
|
||
|
|
[w65c816sxb-hacker](https://github.com/andrew-jacobs/w65c816sxb-hacker) is
|
||
|
|
suitable for this. Note that OF816 currently uses the USB port as the console
|
||
|
|
device.
|
||
|
|
|
||
|
|
You may also create a completely custom ROM image that replaces the WDC monitor
|
||
|
|
with OF816, all that is required (assuming you are not going to use interrupts)
|
||
|
|
is to point the RESET vector to $8000. It may be desirable to point the NMI
|
||
|
|
vector at a routine that resets the system stack pointer and jumps to
|
||
|
|
``_Forth_ui``.
|
||
|
|
|
||
|
|
While this platform provides the "reference" platform with regards to system
|
||
|
|
implementation, configuring it and making it work are an advanced topic.
|
||
|
|
|
||
|
|
**Note:** None of WDC's tools are used to build OF816.
|
||
|
|
|
||
|
|
|
||
|
|
## Port Features
|
||
|
|
|
||
|
|
### Banked ROM Access
|
||
|
|
|
||
|
|
The platform words include ``$SXB-READROM`` ( rom_addr dest_addr size -- ).
|
||
|
|
This word allows copying size bytes from any bank in the ROM into dest_addr.
|
||
|
|
|
||
|
|
The rom_addr is an address of the form $bb00xxxx where bb is the bank number
|
||
|
|
(0-3) and xxxx is the physical address of the memory in bank 0. I.e. the
|
||
|
|
valid ranges are $00008000-$0000FFFF, $01008000-$0100FFFF, etc.
|
||
|
|
|
||
|
|
### FCode/romfs ROM Loader
|
||
|
|
|
||
|
|
If FCode support is enabled, the word ``$SXB-ROMLDR`` is included in the
|
||
|
|
platform words. This encapsulates ``fcode/romloader.fs`` and executing it will
|
||
|
|
cause the ROM Loader and romfs words to be installed (romfs support may be
|
||
|
|
disabled, see the source).
|
||
|
|
|
||
|
|
The ROM Loader keeps a $100-byte cache of the last ROM page read in order to
|
||
|
|
reduce the number of bank-switch/copy operations.
|
||
|
|
|
||
|
|
Once the ROM Loader and romfs are installed, the following words are available:
|
||
|
|
|
||
|
|
#### FCode Loader Words
|
||
|
|
|
||
|
|
``$SXB-ROM-FCODE-AT?`` ( rom-addr -- f ) f is true if there is a FCode magic
|
||
|
|
("MGFC") at the given ROM address. rom-addr must be on a page boundary.
|
||
|
|
|
||
|
|
``$SXB-ROM-BYTE-LOAD`` ( rom-addr -- ) evaluate FCode at rom-addr, satisified
|
||
|
|
by the conditions of ``$SXB-ROM-FCODE-AT?``.
|
||
|
|
|
||
|
|
``$SXB-FC-BOOT`` ( -- ) search ROM at $1000-byte alignments for FCode identified
|
||
|
|
by ``$SXB-ROM-FCODE-AT?`` and evaluate it.
|
||
|
|
|
||
|
|
#### romfs Words
|
||
|
|
|
||
|
|
romfs words generally follow the ANS Forth File Access word set guidelines,
|
||
|
|
however they automatically throw non-zero IORs, therefore if the word returns
|
||
|
|
normally the IOR is always 0. Consult the ANS standard for complete description
|
||
|
|
of stack items.
|
||
|
|
|
||
|
|
``INCLUDE`` ( <>"name" -- ... ) parse name and perform the function of INCLUDED.
|
||
|
|
|
||
|
|
``INCLUDED`` ( c-addr u -- ... ) evaluate romfs file named by c-addr u.
|
||
|
|
|
||
|
|
``OPEN-FILE`` ( c-addr u fam -- fileid 0 ) open romfs file, fam is discarded,
|
||
|
|
access is always read-only.
|
||
|
|
|
||
|
|
``READ-LINE`` ( c-addr u fileid - u2 f 0 ) read a line up to u bytes from file.
|
||
|
|
|
||
|
|
``READ-FILE`` ( c-addr u fileid - u2 0 ) read up to u bytes from file.
|
||
|
|
|
||
|
|
``FILE-POSITION`` ( fid -- u ) return read position in file
|
||
|
|
|
||
|
|
``CLOSE-FILE`` ( fileid -- 0 ) close romfs file
|
||
|
|
|
||
|
|
``ROMFS-LIST`` ( -- ) list files in romfs.
|
||
|
|
|
||
|
|
``$SXB-ROM-ROMFS-AT?`` ( rom-addr -- f ) f is true if there is a ROMFS magic
|
||
|
|
("MGFS") at the given ROM address. rom-addr must be on a page boundary.
|
||
|
|
|
||
|
|
``$SXB-ROMFS`` ( -- u ) VALUE, zero if no romfs was found, otherwise contains
|
||
|
|
the ROM address of the romfs.
|