of816/platforms/W65C816SXB

W65C816SXB

This is a port to WDC's W65C816SXB 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 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.