Detecting a bridge

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Bridges
What it does
Detection
Acorn bridge
SJ bridge

Intro
FileStore
MDFS
Others
Clocks
Interfaces
Misc h/w
Testing
Misc info

Précis

There is little reason to engage in this, unless you wish to manually probe the network, for the NetFS/ANFS automatically handles detection of file servers across bridged networks; and to this end it may be much more productive to issue the SWI NetFS_EnumerateFSList (SWI &40049), perhaps after having issued the SWI NetFS_UpdateFSList (&4004D) with both R0 and R1 set to zero to cause the entire list of known servers to be updated.
Don't forget to call SWI NetFS_EnableCache (&40051) afterwards to allow automatic caching of known servers to resume.

With little more than three calls and a FOR...NEXT loop, you can ascertain which file servers (by name and disc number) are available at which stations on which networks.
The obvious flaw is that each network will require a server, though in reality it would be unusual for a network to not have a file server local to it.

Communicating with the bridge

There are two calls you can send to a bridge.

1. What is our 'local' network?

$buffer%  = "Bridge"
buffer%?6 = reply_port%
buffer%?7 = 0

You should broadcast control byte &82 to port &9C. If any bridge is present, it will reply with two bytes. The first byte will be the local network number, the second byte will be the software running in the bridge.

2. What networks are known about?

$buffer%  = "Bridge"
buffer%?6 = reply_port%
buffer%?7 = network_to_check%

You should broadcast control byte &83 to port &9C. If any bridge is present, the bridge will perform a four-way handshake if the network number is known to it, otherwise it will not reply. Only the bridge which would handle the network specified will respond.
The four-way handshake means the RxCB poll status will be "received", or return code 9.

Putting this into practice

The following program shows how to communicate with a bridge.

REM >checknets
REM
REM Checks our local network, and looks to see what
REM others are available.
REM © 2007 Rick Murray [original from 1999]
REM
REM This version is for RISC OS machines ONLY.
REM
:
checknet% = 0
DIM txcb% 32
DIM rxcb% 32

REM STEP ONE:
REM   Ascertain our 'local' network.

handle% = 0
port% = FNallocateport : REM Also sets 'handle%'

$txcb% = "Bridge"
txcb%?6 = port%
txcb%?7 = 0
SYS "Econet_DoTransmit", &82, &9C, &FF, &FF, txcb%, 8, 2, 3

SYS "Econet_WaitForReception", handle%, 8, 0 TO status%
IF status% = 9 THEN
  PRINT "Our local network is network "+STR$(rxcb%?0);
  PRINT ", bridge software version "+STR$(rxcb%?1)+"."
ENDIF
SYS "Econet_DeAllocatePort", port%


REM STEP TWO:
REM   Look for other networks.

REPEAT
  checknet% += 1

  PRINT "Checking for network "+STR$(checknet%)+"..."+CHR$(13);

  port% = FNallocateport

  $txcb% = "Bridge"
  txcb%?6 = port%
  txcb%?7 = checknet%
  SYS "Econet_DoTransmit", &83, &9C, &FF, &FF, txcb%, 8, 2, 3

  SYS "Econet_WaitForReception", handle%, 8, 0 TO status%
  IF status% = 9 THEN
    PRINT "Network "+STR$(checknet%)+" exists.        "
  ENDIF
  SYS "Econet_DeAllocatePort", port%
UNTIL checknet% = 127
PRINT STRING$(30, " ")'
END
:
:
DEFFNallocateport
  SYS "Econet_AllocatePort" TO port%
  IF port% = &9C THEN
    REM Defeat local loopback...
    SYS "Econet_DeAllocatePort", port%
    SYS "Econet_AllocatePort" TO port%
  ENDIF
  SYS "Econet_CreateReceive", port%, 0, 0, rxcb%, 10 TO handle%
=port%

And for 8 bit machines...

The following program was OCRed and tidied from the MDFS manual, section 10, pages 45-46. It is reproduced here to save you needing to download a 17½Mb archive containing numerous large PDF files - not a viable proposition for those using dial-up access.

Please note that this program may contain errors due to the OCR. I have corrected any that I have found, but some may remain. It's a lot better than the garbled listing in my printed MDFS manual, which misses a big chunk in the middle!

 10 REM Find out what other networks are available
 20 REM (C) 1986, A.J.Engeham, SJ Research
 30 REM ____________________________________________
 40
 50 DIM blk% 100, tx_blk% 20, buffer% 100
 60
 70 osword=&FFF1:osbyte=&FFF4
 80 reply_port=&8A:retries=l0
 90 PROCset_up_rx
100
110 FOR bridge%=l TO 127
120   FOR dummy%=l TO 3
130     PROCbroadcast(bridge%)
140   NEXT
150
160   dummy%=0
170   REPEAT
180     dummy%=dummy%+l
190   UNTIL dummy%=retries OR FNpoll_rx
200
210   IF FNpoll_rx THEN PROCdisplay(bridge%)
220 NEXT
230 PROCdelete
240 PRINT "Finished"
250 END
260
270 DEFPROCset up rx
280   blk%?0=0         : REM control block number put here
290   blk%?1=&7F
300   blk%?2=reply_port
310   blk%!3=&0        : REM Receive from any stations
320   blk%!5=buffer%
330   blk%!9=buffer%+8
340   X%=blk% : Y%=blk% DIV 256
350   A%=&ll
360   CALL osword
370   IF blk%?0=0 THEN PRINT "Can't open a Rx block" : END
380  ENDPROC
390
400 DEFFNpoll_rx
410   A%=&33
420   X%=blk%?0        : REM Get the rx block number
430 =((USR osbyte) AND &8000) <> O
440
450 DEFPROCbroadcast(network%)
460   LOCAL redo
470   redo=5
480
490   REPEAT
500     tx_blk%?0=&83
510     tx_blk%?1=&9C  : REM Broadcast on port &9C
520     tx_blk%!2=&FFFF: REM Broadcast operation
530     $(tx_blk%+4)="BRIDGE"
540     tx_blk%?10=reply_port
550     tx_blk%?11=network%
560     X%=tx_blk% : Y%=tx_blk% DIV 256
570     A%=&10 : CALL osword
580     A%=&32
590     REM Wait for completion
600     X%=FNpoll_tx
610     redo=redo-l
620   UNTIL redo=0 OR X%=&40 OR X%=&43 OR X%=&44 OR X%=0 
630   IF X%>0 THENPRINT"Broadcast fail, error &";~X%:PROCdelete:END
640 ENDPROC
650
660 DEFPROCdelete
670   REM delete a receive block
680   A%=&34
690   X%=blk%?0
700   CALL osbyte
710 ENDPROC
720
730 DEFFNpoll_tx
740   REPEAT UNTIL NOT {(USR osbyte) AND &8000)
750 =(((USRosbyte) AND &FF00) DIV &100)
760
770 DEFPROCdisplay(no%)
780   PRINT "Found network "; no%
790   PROCdelete
800   PROCset_up_rx
810 ENDPROC