BBCBasic won't save/load

[skx]

This happens in both cpmulater and iz-cpm so it might be a porting issue.

Either way resolve it.

[skx]

Suspecting a bug in the BBCBASIC itself.

The following session demonstrates both a load and a save:

BBC BASIC (Z80) Version 3.00  
(C) Copyright R.T.Russell 1987
>load "FOO"

Mistake
>LOAD "FOO"

CP/M Error
>10 PRINT "OK"
>SAVE "STEVE"

CP/M Error
>*CPM

B>exit

In the case of a load we get a single log, shows the file doesn't exist, as expected. Attempting to open a file that does exist we see no further I/O.

For the SAVE call we see only a single call to F_DELETE, there is no subsequent open/write/close. I need to add logging to the F_DELETE call to see which file is even tried to be deleted - but in this case nothing existed anyway.

[skx]

OK Running SAVE "CAKE" results in the single BDOS call:

{"time":"2024-06-21T13:32:13.39065192+03:00","level":"INFO","msg":"BDOS","name":
"F_DELETE","syscall":19,"syscallHex":"0x13","registers":{"A":"13","B":"00","C":"
13","D":"00","E":"5C","F":"3A","H":"3E","L":"00","BC":"0013","DE":"005C","HL":"3
E00"}}
{"time":"2024-06-21T13:32:13.390701097+03:00","level":"DEBUG","msg":"SysCallDeleteFile","glob":"CAKE.BBC"}

Which is crazy. I think not a bug in the emulator, just in the binary. Will investigate sources to take it further:

• https://github.com/jblang/bbcbasic-z80/tree/master

[skx]

OK this change lets us get further:

index c5c3004..ee23c85 100644
--- a/cpm.asm
+++ b/cpm.asm
@@ -433,7 +433,7 @@ INCRDF:     CALL    INCSEC
 READ:  CALL    SETDMA
        LD      A,33
 BDOS1: CALL    BDOS0           ;*
-       JR      NZ,CPMERR       ;*
+;      JR      NZ,CPMERR       ;* - steve
        OR      A               ;*
        RET                     ;*
 CPMERR:        LD      A,255           ;* CP/M 3

Looks like it is expecting the zero flag to be set for some reason, when calling CP/M.

Now we fail with a better error and cake.bbc was created:

A>b:
B>bbcbasic
BBC BASIC (Z80) Version 3.00  
(C) Copyright R.T.Russell 1987
>10 PRINT "CAKE"
>SAVE "CAKE"
{"time":"2024-06-21T13:55:37.554230916+03:00","level":"ERROR","msg":"Unimplemented BDOS Syscall","syscall":40,"syscallHex":"0x28"}

Error running CCP: UNIMPLEMENTED

That means I need to add support for:

BDOS function 40 (F_WRITEZF) - Write random with zero fill Supported by: CP/M 2.2 and later.

Entered with C=28h, DE=FCB address. Returns error codes in BA and HL.

As function 34, but if the write is to a newly allocated disc block the remainder of the block is filled with zeroes.

[skx]

Success!

• Patched BBC basic to ignore the flag.
• Implemented the missing syscall.

Now it works:

(C) Copyright R.T.Russell 1987
>10 PRINT "SAVED?"
>SAVE "CAKE"
>LIST
   10 PRINT "SAVED?"
>NEW
>LIST
>LOAD "CAKE"
>LIST
   10 PRINT "SAVED?"
>

[skx]

Realized the real issue isn't to do with A-register, or Z-flag, instead it is the 16 bit return value which is expected.

Reopening for a fix that doesn't require any binary change to BBCBASIC.COM