CustomDNFS 1.30
			     ===============
			       J.G.Harston
		70 Camm Street, Walkley, Sheffield S6 3TR
			  jgh@arcade.demon.co.uk

Most BBC models Bs use DNFS 3.00 which contains DFS 1.20 and NFS 3.60. 
DFS 1.20 interfaces with the 8271 floppy disk controller and has many
inprovements and major corrections from DFS 0.90.  NFS 3.60 has many major
corrections from the previous main release 3.34.

The NFS defaults to a fileserver at station 0.254 and a printer server at
station 0.235.  Many systems have a printer server at the same station as
the file server, and on a network with multiple bridges, this would mean
keeping BBCs on the same subnet as the fileserver.  This program allows
you to change these default setting.

There is a slight problem with DFS 1.20 if you use it with 3.5" disk
drives.  Various factors come together to cause the 8271 to return 'Disk
error 10' (Drive not ready) errors.  This program allows you to insert a
patch so that disk access always waits until the drives are ready.  This
results in DFS 1.21. The program DFSTester will thrash DFS by saving and
loading lots of data and can be used to confirm that DFS is reading and
writing data correctly.

To use CustomDNFS you need a ROM image of DNFS.  CustomDNFS can read the
DNFS ROM active in the machine, or you can use the supplied *SrSave
command to save it directly to disk. You need to know which ROM slot you
have DNFS in.  If you have a *ROMs command, this will tell you. 
Otherwise, the easiest way to find out is to look inside.  The ROM sockets
are at the front of the PCB just under the keyboard to the right.  Slot 15
is the rightmost one, and they count down to 12 going to the left.  If the
DNFS ROM is in slot 14 (&E in hex), then use *SrSave to save the ROM image
as follows:

	*SrSave DNFS 8000+4000 E

When you run CustomDNFS you will be asked if you want to read DNFS from
the active ROM.  If you answer 'N' you will instead be asked for the name
of the ROM image to load.  At this prompt you can also do *commands.  If
you just press RETURN, the displayed default of 'DNFS3-00' will be used.

You will then be shown what the current settings are as follows:

		   Customise DNFS for BBC B/B+
		   ===========================

		Machine type:  &0001 - Acorn BBC

		NFS version:    3.60

		Fileserver:     000.254

		Printer server: 000.235

		DFS version:    DFS 1.20

Pressing RETURN will move between each option.  Entering a new value or
YES to the 'Change to fix timeouts?' prompt for DFS will update that
option.  The fileserver and the printer server must be on the same
network.  Changing either will change both.

If the image loaded is an 8K NFS ROM, the DFS option will be disabled.

When entering 'Yes' to the 'Ok?' prompt the program asks for the name to
save the new image as.  At this prompt you can do *commands.  If you just
press RETURN, the displayed default of the loaded filename changed to end
with '01' will be used.  This can now be blown into an EPROM and fitted
permanently.

Technical Information
=====================
The DFS 1.21 patch works by adding a check at the end of the disk access
code. This checks if the result is 'Not ready', and if it is, clears it and
retries continuously until a result other than 'Not Ready' is returned. The
patch code is as follows:

A504 EQUS "COMPACT"
A50B EQUB &BB  ; Routine address-1        EQUB &BB  ; Trim routine to
A50C EQUB &1D                             EQUB &20  ; make space

AA4C LDY #&2B                             DEC &A2   ; Dec. retries
AA4E DEC &A2   ; Dec. tries               BMI &AAC7 ; <0, jump to release
AA50 BMI &AAC7 ; <0, jump to release      JSR &BB15 ; Verify 00:8+2 and
                                                    ; reset 'Not Ready'
AA52 JSR &ACA4 ; verify 00:8+2            CMP #0    ; Check result
AA55 BNE &AA4C ; Loop back with error

AC0E JSR &ACA7 ; Wait until action done
AC11 BNE &AC32 ; Result<>0, retry         BNE &AC2D ; Result<>0, retry
AC13 JSR &ABC7 ; Set retries to 10
AC16 INC &CE   ; Increment track
AC18 LDA #&00
AC1A STA &CF   ; Set sector to zero
AC1C LDA &107C ; Get number
AC1F CLC
AC20 ADC &1073 ; &1072-5=&1072-5+number*256
AC23 STA &1073
AC26 BCC &AC4B
AC28 INC &1074
AC2B BNE &AC4B                            BCS &AC4B ; Jump to do next
AC2D INC &1075                            JSR &BB0D ; Reset 'Not Ready'
AC30 BCS &AC4B ; Jump to do next          BEQ &AC39 ; Jump to try again
                                                    ; if 'Not Ready'
;
AC32 DEC &A2   ; Dec. tries
AC34 BPL &AC39 ; Try again
AC36 JMP &AAC7
;
AC39 LDY #&04  ; Copy command back to &A3-A7

BADD                                      ; Shortened help strings

BB0D                                      PHA       ; Save result
                                          JSR &AA84 ; Reset 'Not Ready'
                                          PLA       ; Get result back
                                          CMP #&10  ; Is it 'Not Ready'?
                                          RTS
                                          ;
BB15                                      LDY #&2B
                                          JSR &ACA4 ; Verify track 0
                                          JSR &BB0D ; Reset 'Not Ready'
                                          BEQ &BB15 ; Loop if 'Not Ready'
                                          RTS
                                          ;
                                          NOP        ; Spare byte
BB21                                      JSR &A9CE  ; Shortened *COMPACT
                                                     ; routine
                                          JSR &9FF7
                                          EQUS "Compact :"
                                                     ; removed "ing"

Version History
===============
23-08-1998 v1.30 JGH: Will read DNFS from active ROM.
06-06-1998 v1.20 JGH: Timeouts fix for DFS added, default filename
			offered, checks loaded file appears to be DNFS. 
			Checks if only 8K NFS ROM.
20-11-1997 v1.10 JGH: Allows customisation of NFS default settings for
			machine type, version, fileserver station and
			printer server station.