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This Technical Note discusses known errors and omissions in Inside
Macintosh: Networking.
[Sep 01 1994]
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Topics
- Clarification to the use of the
GetBridgeAddress function. Sept 94
- Corrected special considerations to the use of
PSetSelfSend.
- Socket Listener sample code correction/modification. Sept 94
- "Corrected"
EParamMisc2 C interface declaration is incorrect, Chapter 11 Sept 94
- ATP
transID transaction ID field omitted Sept 94
Back to top Chapter 2 - About the AppleTalk Utilities
Clarification to the use of GetBridgeAddress
Page 2-6, Getting the Address of Your Node or Your Local Router
The documentation states that "to get the node ID part of a local router's
address, you can call the GetBridgeAddress function." This statement is not
correct. Instead of returning the actual node ID of the router, the
GetBridgeAddress function returns a non-zero function result if a router exists
on the network. A function result of zero indicates that there is no router.
To get the node ID of the router, use the PGetAppleTalkInfo function instead.
Correction to the Description for PSetSelfSend
Page 2-16, PSetSelfSend description.
The documentation states that "Sending packets between a multinode application
and user node applications on the same machine is independent of the intranode
delivery feature. A multinode is treated as a virtual node distinct from the
user node...". These statements lead to the incorrect conclusion that one
does not need to set the SelfSend capability to send packets between the user
node and the multinode. To send packets between the user node and a multinode,
use PSetSelfSend to turn on intranode delivery service.
Back to top Chapter 6 - AppleTalk Transaction Protocol (ATP)
Transaction ID field transID omitted
The transID field should be used in place of the reqTID field
as shown in the following areas:
Page 6-15
"The request transaction ID transID that ATP assigns to this request.
If you intend to respond to the request, save this value because you will need to pass
it to the PSendResponse function and the PAddResponse function to
identify the request for which the response message is intended..."
Page 6-16
"For the input address block (addrBlock) and transaction ID
(transID) parameters to PSendResponse, use the address block
(addrBlock) and request transaction ID (transID) parameter
values that the PGetRequest function returned."
Page 6-33
PGetRequest parameter block and description should look as follows:
Parameter block
-> ioCompletion ProcPtr A pointer to a completion routine.
<- ioResult OSErr The function result.
<- userData LongInt Four bytes of user data.
-> csCode Integer Always getRequest for this function.
-> atpSocket Byte The socket number.
<- atpFlags Byte The control information.
<- addrBlock LongInt The destination socket address.
<-> reqLength Word On input, the request buffer size. On return,
the actual of the request received.
-> reqPointer Ptr A pointer to the request buffer.
<- bitMap Byte A bitmap.
<- transID Word The transaction ID.
Field descriptions
transID The transaction ID of the request that PGetRequest has
received. ATP supplies this value.
"The PGetRequest function returns the transaction ID of the request
that it receives in the transID field. You should save this value if
you intend to respond to the request; this transaction ID is used as an input
parameter to the PSendResponse and PAddResponse functions. To
determine that the request transaction ID specified in the transID
field is valid, first check the atpTIDValidvalue bit (bit 1) of the
atpFlags field. If this bit is set, the transID field value
is valid."
Page 6-37
Field descriptions
transID The transaction ID of the request for which this response is meant.
Page 6-43
Field should be an Integer, not a Byte:
-> transID Integer The transaction ID of the request with which the
PSendResponse function to be canceled is associated.
Page 6-48
Add the transID field to the GetRequestParm parameter block
as follows:
GetRequestParm:
(bitMap: Byte; {bitmap}
filler1: Byte;
transID: Integer);
Page 6-57
Add the transID field to the GetRequest Parameter Variant as follows:
GetRequest Parameter Variant
22 reqTID word request transaction ID
26 csCode word command code; always getRequest
29 atpFlags byte control information
30 addrBlock long destination socket address
34 reqLength word request size in bytes
36 reqPointer long pointer to request data
44 bitMap byte current bitmap
46 transID word request transaction ID
Back to top Chapter 7 - Datagram Delivery Protocol (DDP)
Listing 7-6 Socket Listener sample code correction/modification.
Page 7-26 through 7-30, Receiving and processing a DDP packet
The sample code is provided to demonstrate a generic socket listener written in
68000 Assembler. The supplied code in this chapter does not correctly process
a packet which is received with a checksum. A BRA.S instruction bypasses the
portion of code which checks the packet for a checksum. In addition, the code
for processing the checksum was not included in this release of Inside
Macintosh: Networking. There is one other correction relating to the
GetNextBuffer code. Before calling DeQueue, we must check for a nil pointer as
DeQueue in some releases of System Software does not do this for us. The
following is the complete socket listener code sample, including the
SL_DoChksum code. Corrections to the supplied code for the socket
listener only are presented in bold typeface.
In addition, the code has been modified to compile as a code resource which can
be called using a Universal ProcPtr and executed in mixed mode, to facilitate
compilation as native Power Macintosh code. The beginning of the code resource
is the socket listener entry point, which is a JMP instruction to the actual
listener code. The initialization code for the listener is two bytes into the
code resource. For an example use of this listener code, refer to the Network
Watch (DMZ) v1.3 application which is available on the Developer CD (Tool Chest
Edition), August 1994 or later.
INCLUDE 'QuickEqu.a'
INCLUDE 'ToolEqu.a'
INCLUDE 'SysEqu.a'
INCLUDE 'ATalkEqu.a'
INCLUDE 'Traps.a'
INCLUDE 'SysErr.a'
;
;
; Record Types
;
;_________________________________________________________________________
MyQHdr RECORD 0
qFlags DS.W 1
qHead DS.L 1
qTail DS.L 1
ENDR
PacketBuffer RECORD 0
qLink DS.L 1
qType DS.W 1
buffer_Type DS.W 1 ; DDP Type
buffer_NodeID DS.W 1 ; Destination node
buffer_Address DS.L 1 ; Source address in AddrBlock format
buffer_Hops DS.W 1 ; Hop count
buffer_ActCount DS.W 1 ; length of DDP datagram
buffer_CheckSum DS.W 1 ; Chksum error returned here
; (cksumErr or noErr)
buffer_Ticks DS.L 1 ; TickCount when handler called
buffer_Data DS.B ddpMaxData ; the DDP datagram
ENDR
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THE_LISTENER PROC EXPORT
BRA.S TheListener
BRA.S SL_InitSktListener ; branch to init code
;_________________________________________________________________________
;
; Local Variables
;
;_________________________________________________________________________
free_queue DC.L 0 ; pointer to freeQ QHdr - init'd by InitSktListener
used_queue DC.L 0 ; pointer to usedQ QHdr - init'd by InitSktListener
current_qelem DC.L 0 ; pointer to current PacketBuffer record
; initialized by InitSktListener, then
; set by socket listener after every packet.
; NIL if no buffer is available.
;_________________________________________________________________________
; Function SL_InitSktListener(freeQ, usedQ: QHdrPtr): OSErr
;
StackFrame RECORD {A6Link},DECR ; build a stack frame record
Result1 DS.W 1 ; function's result returned to caller
ParamBegin EQU * ; start parameters after this point
freeQ DS.L 1 ; freeQ parameter
usedQ DS.L 1 ; usedQ parameter
ParamSize EQU ParamBegin-* ; size of all the passed parameters
RetAddr DS.L 1 ; placeholder for return address
A6Link DS.L 1 ; placeholder for A6 link
LocalSize EQU * ; size of all the local variables
ENDR
SL_InitSktListener:
WITH StackFrame,MyQHdr ; use these record types
LINK A6,#LocalSize ; allocate our local stack frame
; copy queue header pointers into our local storage for use in the listener
LEA used_queue,A0 ; copy usedQ into used_queue
MOVE.L usedQ(A6),(A0)
LEA free_queue,A0 ; copy freeQ into free_queue
MOVE.L freeQ(A6),(A0)
; dequeue the first buffer record from freeQ and set current_qelem to it
MOVEA.L freeQ(A6),A1 ; A1 = ^freeQ
LEA current_qelem, A0 ; copy freeQ.qHead into
; current_qelem
MOVE.L qHead(A1),(A0)
MOVEA.L qHead(A1),A0 ; A0 = freeQ.qHead
_Dequeue
MOVE.W D0,Result1(A6) ; Return status
@1 UNLK A6 ; destroy the link
MOVEA.L (SP)+,A0 ; pull off the return address
ADDA.L #ParamSize,SP ; strip all of the caller's
; parameters
JMP (A0) ; return to the caller
;_________________________________________________________________________
;
; SL_TheListner - process packets received at the designated socket
;
; Input:
; D0 (byte) = packet's destination socket number
; D1 (word) = number of bytes left to read in packet
; A0 points to the bytes to checksum
; A1 points to the bytes to checksum
; A2 points to MPP's local variables
; A3 points to next free byte in Read Header Area
; A4 points to ReadPacket and ReadRest jump table
;
; Return:
; D0 is modified
; D3 (word) = accumulated checksum
;_________________________________________________________________________
IMPORT SL_DoChksum : code
TheListener:
WITH PacketBuffer
; get pointer to current PacketBuffer
GetBuffer:
LEA current_qelem,A3 ; get the pointer to the PacketBuffer to use
MOVE.L (A3),A3
MOVE.L A3,D0 ; if no PacketBuffer
BEQ.S NoBuffer ; then ignore packet
; read rest of packet into PacketBuffer.datagramData
MOVE.L D1,D3 ; read rest of packet
LEA buffer_data(A3),A3 ; A3 = ^bufferData
JSR 2(A4) ; ReadRest
BEQ.S ProcessPacket ; If no error, continue
BRA RcvRTS ; there was an error, so ignore packet
; No buffer; ignore the packet
NoBuffer CLR D3 ; Set to ignore packet (buffer size = 0)
JSR 2(A4) ; ReadRest
BRA GetNextBuffer ; We missed this packet, but maybe there
; will be a buffer for the next packet...
; Process the packet you just read in.
; ReadRest has been called so registers A0-A3 and D0-D3 are free to use.
; We'll use registers this way:
PktBuff EQU A0 ; the current PacketBuffer
MPPLocals EQU A2 ; pointer to MPP's local variables (still set
; up from entry to socket listener)
HopCount EQU D0 ; used to get the hop count
DatagramLength EQU D1 ; used to determine the datagram length
SourceNetAddr EQU D2 ; used to build the source network address
ProcessPacket:
LEA current_qelem,PktBuff ; PktBuff = current_qelem
MOVE.L (PktBuff),PktBuff
; do everything that's common to both long and short DDP headers
; first, clear buffer_Type and buffer_NodeID to ensure their high bytes are 0
CLR.W buffer_Type(PktBuff) ; clear buffer_Type
CLR.W buffer_NodeID(PktBuff) ; clear buffer_NodeID
; clear SourceNetAddr to prepare to build network address
MOVEQ #0,SourceNetAddr ; build the network address in
; SourceNetAddr
; get the hop count
MOVE.W toRHA+lapHdSz+ddpLength(MPPLocals),HopCount ; Get hop/length
; field
ANDI.W #DDPHopsMask,HopCount ; Mask off the hop count bits
LSR.W #2,HopCount ; shift hop count into low bits of
; high byte
LSR.W #8,HopCount ; shift hop count into low byte
MOVE.W HopCount,buffer_Hops(PktBuff) ; and move it into the
; PacketBuffer
; get the packet length (including the DDP header)
MOVE.W toRHA+lapHdSz+ddpLength(MPPLocals),DatagramLength ; Get length field
ANDI.W #ddpLenMask,DatagramLength ; Mask off the hop count bits
; now, find out if the DDP header is long or short
MOVE.B toRHA+lapType(MPPLocals),D3 ; Get LAP type
CMPI.B #shortDDP,D3 ; is this a long or short DDP
; header?
BEQ.S IsShortHdr ; skip if short DDP header
; it's a long DDP header
MOVE.B toRHA+lapHdSz+ddpType(MPPLocals),buffer_Type+1(PktBuff)
; get DDP type
MOVE.B toRHA+lapHdSz+ddpDstNode(MPPLocals),buffer_NodeID+1(PktBuff)
; get destination node from LAP
; header
MOVE.L toRHA+lapHdSz+ddpSrcNet(MPPLocals),SourceNetAddr
; source network in hi word
; source node in lo byte
LSL.W #8,SourceNetAddr ; shift source node up to high
; byte of low word
; get source socket from DDP
; header
MOVE.B toRHA+lapHdSz+ddpSrcSkt(MPPLocals),SourceNetAddr
SUB.W #ddpType+1,DatagramLength ; DatagramLength = number of bytes
; in datagram
;BRA.S MoveToBuffer <Delete this statement>
; Determine if there is a checksum
TST.W toRHA+lapHdSz+ddpChecksum(MPPLocals) ;Does packet have checksum?
BEQ.S noChecksum
; Calculate checksum over DDP header
MOVE.W DatagramLength,-(SP) ; save DatagramLength (D1)
CLR D3 ; set checksum to zero
MOVEQ #ddphSzLong-ddpDstNet,D1 ; D1 = length of header part to
; checksum pointer to dest network
; number in DDP header
LEA toRHA+lapHdSz+ddpDstNet(MPPLocals),A1
JSR SL_DoChksum ; checksum of DDP header part
; (D3 holds accumulated checksum)
; Calculate checksum over data portion (if any)
LEA buffer_Data(PktBuff),A1 ; pointer to datagram
MOVE.W (SP)+,DatagramLength ; restore DatagramLength(D1)
MOVE.W DatagramLength,-(SP) ; save DatagramLength (D1)
; before calling SL_DoChksum
BEQ.S TestChecksum ; don't checksum datagram if its
; length = 0
JSR SL_DoChksum ; checksum of DDP datagram part
; (D3 holds accumulated checksum)
TestChecksum:
MOVE.W (SP)+,DatagramLength ; restore DatagramLength(D1)
; Now make sure the checksum is OK.
TST.W D3 ; is the calculated value zero?
BNE.S NotZero ; no -- go and use it
SUBQ.W #1,D3 ; it is 0; make it -1
NotZero:
CMP.W toRHA+lapHdSz+ddpChecksum(MPPLocals),D3
BNE.S ChecksumErr ; Bad checksum
MOVE.W #0,buffer_CheckSum(A0) ; no errors
BRA.S noChecksum
ChecksumErr:
MOVE.W #ckSumErr,buffer_CheckSum(PktBuff) ; checksum error
noChecksum:
BRA.S MoveToBuffer
; it's a short DDP header
IsShortHdr:
; get DDP type
MOVE.B toRHA+lapHdSz+sddpType(MPPLocals),buffer_Type+1(PktBuff)
; get destination node from LAP
; header
MOVE.B toRHA+lapDstAdr(MPPLocals),buffer_NodeID+1(PktBuff)
; get source node from LAP header
MOVE.B toRHA+lapSrcAdr(MPPLocals),SourceNetAddr
LSL.W #8,SourceNetAddr ; shift src node up to high byte
; of low word
; get source socket from short DDP
; header
MOVE.B toRHA+lapHdSz+sddpSrcSkt(MPPLocals),SourceNetAddr
; DatagramLength = number of bytes in
; datagram
SUB.W #sddpType+1,DatagramLength
MoveToBuffer:
;move source network address into PacketBuffer
MOVE.L SourceNetAddr,buffer_Address(PktBuff)
; move datagram length into PacketBuffer
MOVE.W DatagramLength,buffer_ActCount(PktBuff)
; Now that we're done with the PacketBuffer, enqueue it into the usedQ and get
; another buffer from the freeQ for the next packet.
LEA used_queue,A1 ; A1 = ^used_queue
MOVE.L (A1),A1 ; A1 = used_queue (pointer to usedQ)
_Enqueue ; put the PacketBuffer in the usedQ
GetNextBuffer:
LEA free_queue,A1 ; A1 = ^free_queue
MOVE.L (A1),A1 ; A1 = free_queue (pointer to freeQ)
LEA current_qelem, A0 ; copy freeQ.qHead into current_qelem
MOVE.L qHead(A1),(A0)
MOVEA.L qHead(A1),A0 ; A0 = freeQ.qHead
MOVE.L A0,D0 ; check whether there is a queue element
BEQ.S RcvRTS ; branch if not - don't dequeue nil ptr.
_Dequeue
RcvRTS:
RTS ; return to caller
ENDWITH
ENDP
;_________________________________________________________________________
;
; SL_DoChksum - accumulate ongoing checksum (from Inside Macintosh)
;
; Input:
; D1 (word) = number of bytes to checksum
; D3 (word) = current checksum
; A1 points to the bytes to checksum
;
; Return:
; D0 is modified
; D3 (word) = accumulated checksum
;_________________________________________________________________________
SL_DoChksum PROC
CLR.W D0 ; Clear high byte
SUBQ.W #1,D1 ; Decrement count for DBRA
ChksumLoop:
MOVE.B (A1)+,D0 ; read a byte into D0
ADD.W D0,D3 ; accumulate checksum
ROL.W #1,D3 ; rotate left one bit
DBRA D1,ChksumLoop ; loop if more bytes
RTS
ENDP
END
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Listing 7-7 sample code has logic error
Page 7-32, Testing for Available Packets
The sample code "Determining if the socket listener has processed a packet",
incorrectly uses the following statement to check whether a packet was
successfully Dequeued:
IF (Dequeue(QElemPtr(bufPtr), @usedQ) <> noErr) THEN
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The corrected statement is:
IF (Dequeue(QElemPtr(bufPtr), @usedQ) = noErr) THEN
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Back to top Chapter 11 - Summary of Ethernet, TokenRing, and FDDI
"Corrected" EParamMisc2 C interface declaration is incorrect
Page 11-46, A corrected definition for the EParamMisc2 variable type is presented as:
typedef struct {
EParamHeader
char eMultiAddr[5];
} EParamMisc2;
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This declaration is incorrect. The eMultiAddr field is 6 bytes long.
The correct structure is defined as:
typedef struct {
EParamHeader
char eMultiAddr[6];
} EParamMisc2;
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Back to top References
Inside Macintosh: Networking
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