Memory Spaces (ROM/RAM)
Words that act on memory in the target can either reference the RAM (read/write) or the ROM (read-only). The available data space is dependent on whether it is being accessed during compile-time or run-time.
Compile-time
During compile-time, you’ll reference RAM by default. You’re able to
select the affected data space using ROM and RAM for some words.
This is the only time where the ROM is writable (since gbforth is generating the program), and generally speaking, this is where you want to store most of your data.
| Word | Memory |
|---|---|
@ |
ROM |
c@ |
ROM |
! |
ROM |
c! |
ROM |
, |
ROM |
c, |
ROM |
here |
ROM/RAM |
unused |
ROM/RAM |
allot |
ROM/RAM |
align |
ROM/RAM |
aligned |
ROM/RAM |
create |
ROM/RAM |
variable |
ROM/RAM |
As you can see, you are not able to initialise, read from or write to the RAM at
compile-time. Keep in mind that you can only reserve space in the RAM (and
name the space with words such as CREATE and VARAIBLE), but gbforth will
not initialise (or zero) this memory for you.
If you need to initialise the RAM, you’ll need to do this at run-time (meaning you might have to store some data in the ROM, and then copy it over on startup).
Run-time
During run-time, you are unable to modify the ROM, so you always reference
the RAM when trying to write or allocate memory. As such, the words ROM
and RAM are not available here.
The ROM is still accessible for reading, but since @ and c@ read from a
specific memory address, the memory space is implicit.
Additionally, words like CREATE and VARIABLE are not available due to the
target not having an input steam to parse the name from.
| Word | Memory |
|---|---|
@ |
ROM/RAM |
c@ |
ROM/RAM |
! |
RAM |
c! |
RAM |
, |
RAM |
c, |
RAM |
here |
RAM |
unused |
RAM |
allot |
RAM |
align |
RAM |
aligned |
RAM |
create |
unavailable |
variable |
unavailable |