OS_File 255

Not sure if this is a bug. Certainly looks like it. Nothing serious though I don’t think.

I’ve got a bit of code that loads a file into memory and
works fine. Just simple standard stuff

MOV R0,#255
ADR R1,Address Of My Filename
ADR R2,Address To Load My File
MOV R3,#0
SWI “XOS_File”

My question is if the file doesn’t exist the documentation
at :

https://www.riscosopen.org/wiki/documentation/show/OS_File%20255

says that R0 = 0 but in my case it returns an address that
has an error string. Am I looking at outdated documentation or am I correct or is there something else going on. Should I be testing R0 >3 to imply the file doesn’t exist as R0, according to same documentation, should return 0 – 3 for the object type.

The documention says An error will be generated if the file is not found, is a directory, no read access, or a bad load address.

Which means, as is common with most SWIs, if the V flag is set on exit, then R0 will be a pointer to an error block. It isn’t specifically mentioned in the documentation for each call because it is something that applies to all of them.
https://www.riscosopen.org/wiki/documentation/show/SWI%20Error%20Block
http://www.riscos.com/support/developers/prm/errors.html

Yes Rick, I am aware of the V flag again, i’d forgotten that to be fair.
I was merely wondering if the documentation for OS_File 255 was misleading as it clearly states R0 returns holding the object type of which 0 = object not found.

https://www.riscosopen.org/wiki/documentation/show/File%20Object%20Types

Yet when my code above is run it does not return a 0. It
will crash, obviously, if I use the command without the X but as it is,
with the X, it does not return a 0.

As an afterthought, when I get a dump of the registers and flags, are
the flags set if they are in capitals or lower case. In my code example
above I am getting the V flag in lower case if object is not found.

The wiki page on “File Object Types” is used by 19 other pages besides “OS_File 255”. It is reasonable to suppose that one or more of those do indeed make use of object type 0 meaning “not found”, but as already mentioned OS_File 255 returns an error instead.

Ahh. Okay then Stuart that makes more sense. Thats cleared that up. No need to wonder anymore.

In my code example above I am getting the V flag in lower case if object is not found.

That would be rather odd. ;-)

>AUTO
   10DIM x% 255
   20SYS "XOS_File", 255, "$.nofilehere", x%, 0 TO r0% ; f%
   30PRINT r0%, f%, (f% AND 1)
   40OSCLI("Memory "+STR$~r0%+" +20")
>RUN
 536880196         5         1

Address  :     7 6 5 4     B A 9 8     F E D C     3 2 1 0 :    ASCII Data
20002444 :    000000D6    656C6946    2E242720    69666F6E : Ö...File '$.nofi
20002454 :    6568656C    20276572    20746F6E    6E756F66 : lehere' not foun
>

@Greg – I think you may be trying *ShowRegs? That register dump isn’t modified simply because a SWI is returning a V-set error.

Oops. My bad gentlemen. Eyes wern’t working. Capital V to show V flag is set. Promise I will double check my homework before handing in next time :-)