Date   : Thu, 31 Jan 1985 12:38:42 PST (Thu)
From   : Bridger Mitchell <bridger@Rand-Unix.ARPA>
Subject: Re: PUBPATCH and "swiped files"

PUBPATCH *MUST* be installed on a STANDARD cp/m 2.2 bdos!

Jan Steinman and Paul Kelley have both reported similar problems--
files disappearing from the disk directory following the first
directory entry with 'E5' in byte 0.

Paul's problem was that his Heath CP/M 2.2.03 was *NOT* a standard
cp/m 2.2 bdos.  It contained this patch, abstracted by Paul:

;Patch at BDOS+0DEEH - End of BDOS
;Come here from GETALOC when first byte marked erased
;Speeds up allocation calculation
PATCH: INX     H               ;look at second byte
       CMP     M
       JNZ     GETA1           ;if not erase mark, assume file entry
                               ;  and continue checking directory
       RET                     ;else assume we have found the region of
                               ;  the directory not changed since formatting
                               ;  and quit checking

               **************************
As we said in Dr. Dobbs, and in the PUBPATCH.ASM source, PUBPATCH
patch must be installed in a  *COMPLETELY STANDARD CP/M 2.2 BDOS!*
               **************************

Please recheck your bdos.  In the Heath case, Paul's version looked
like this:

Fragment from STANDARD BDOS2.2 routine to get the allocation vector
;
GETA1: MVI     C,0FFH          ;set the exit code
       CALL    NXTDIR          ;set the next directory pointers
       CALL    CHKCNT          ;was there one?
       RZ                      ;return if not
       CALL    PNTDIR          ;point to the right spot
;HL now points to first byte of directory entry in DIRBUF
       MVI     A,DELDAT        ;get the file deleted mark
       CMP     M               ;is this what we see?
       JZ      GETA1           ;keep looking for a nonempty block
       LDA     USRCOD          ;get the user byte
       CMP     M               ;test this against the first byte
       JNZ     GETA2           ;if we don't match mark this block

;Fragment from HEATH BDOS2.2 routine to get the allocation vector
;
GETA1: MVI     C,0FFH          ;set the exit code
       CALL    NXTDIR          ;set the next directory pointers
       CALL    CHKCNT          ;was there one?
       RZ                      ;return if not
       CALL    PNTDIR          ;point to the right spot
;HL now points to first byte of directory entry in DIRBUF
       MVI     A,DELDAT        ;get the file deleted mark
       CMP     M               ;is this what we see?
--->        JZ      PATCH           ;TEST FOR FORMAT AREA
       LDA     USRCOD          ;get the user byte
       CMP     M               ;test this against the first byte
       JNZ     GETA2           ;if we don't match mark this block

Jan:   Please let me know if this is, in fact, the source of your
       problem.
                               
info-cpm list:
       The Heath code seems risky to me:  Anyone who, e.g., uses
       DU to clear a bad directory entry to E5's will end up
       unwittingly wiping out the rest of his directory.


--bridger mitchell