6502/VolksForth
1
0
Fork 0
mirror of https://github.com/forth-ev/VolksForth.git synced 2024-12-22 06:29:17 +00:00
Code Issues Projects Releases Wiki Activity

Merge pull request #28 from pzembrod/target-vfvm

Browse Source 
Some vfvm design thoughts and questions
This commit is contained in:
Carsten Strotmann 2020-11-24 13:56:59 +00:00 committed by GitHub
commit a052644fba
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 19 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
vfvm/README.org
View File

@ -20,3 +20,22 @@
* opcodes $0100-$FEFF -> implicit jump to subroutine
- allows easy implementation of ITC and DTC Forth
* memory $FFF0-$FFFF -> memory mapped I/O, Bankswitching etc
* Design questions and thoughts
* implicit jump to subroutine opcode(s)
* would use the Forth Return Stack?
* with 16bit alignment, should we use opcode bit 0 for implicit
return from subroutine?
* pros: obvious, space and time saved
* cons: a compiled word would have different values with and
without following RTS. Some code may depend on the same word
always having the same compile token.
* that would mean non NEST or UNNEST routines, but NEST and UNNEST
would be primitives, UNNEST even a 0-byte primitive if we do the
bit 0 thing?
* would not having a NEST routine influence compatibility with ITC
VolksForth flavours? Would a colon definition then look just like
a Code definition, with in both cases the CFA pointing to the PFA?
* would the address of the implicit JSR be the CFA or the PFA of the
called code?