[Oberon] SYSTEM.PTR vs SYSTEM.ADDRESS

[thutt at harp-project.com]

Joerg writes:

 > I can only guess what SYSTEM.PTR and SYSTEM.ADDRESS are; I assume
 > these are TYPEs with special compatibility rules. As those are not
 > defined in Oberon but by your compiler, please consult your
 > compiler’s manual for details.

SYSTEM.PTR is a generic pointer type.  It can be assigned any other
pointer type, and is most often (in my experience) used to accept
generic pointers as a procedure parameter.   There are uses of
SYSTEM.PTR in Fonts.Mod (to gain access to font data loaded in a
system block of memory), Display.Mod (to allocate system blocks of
memory for display patterns), and in Types.Mod (to gain access to
internal information about a pointer's type at runtime).

I don't know have any information about implementation of
SYSTEM.ADDRESS.


 >
 > SYSTEM.PUT and SYSTEM.GET are low level procedures used to directly
 > manipulate memory or HW registers.

I think SYSTEM.GETREG and SYSTEM.PUTREG are generally for getting and
setting machine registers.  PUT and GET are used to directly access
memory (escaping the Oberon language safety).

 > Typically used in device
 > drivers.  SYSTEM.GET(adr, w) is the same as w := adr^ „adr“ being
 > an absolute memory address.  How your memory layout and your memory
 > mapped IO registers look like depends on your HW system you run
 > Oberon on.

--
With sadness in my heart and joy in my mind
I thought about the ghosts that we left behind.
              -- Not My Slave (Oingo Boingo)