Path: utzoo!utgpu!watserv1!watmath!att!mcdchg!mcdhup!mergvax!mergsun!ting
From: ting@mergsun.UUCP (Steve Ting)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Surviving a Bus Error
Message-ID: <180@mergsun.UUCP>
Date: 19 Mar 90 16:02:53 GMT
References: <1990Mar13.192544.1617@asterix.drev.dnd.ca>
Organization: Linotype Co., Hauppauge N.Y.
Lines: 114

From article <1990Mar13.192544.1617@asterix.drev.dnd.ca>, by louis@asterix.drev.dnd.ca (Louis Demers):
> Hi,
> 
> Background:
> 	We are developing a piece of lab equipment which is controlled by
> 	a Macintosh  II.  We developed our own controllers which will be
> 	interfaced to the mac using GreenSpring IO card and some custom
> 	Industry Pack.  The control registers can be configured at
> 	different addresses.
> 
> Problems:
> 	When we access one of the registers and the controllers is not
> 	turned on, we crash with a bus errors.  We suffer the same faith
> 	when we access the registers at the wrong address.
> 
> Wish:
> 	I wish I could try to access an address and if the controller
> 	were turned off or not at this particular address, I would like to
> 	tell the user to check the power to the card or the address
> 	configuration.  This could take the form of a subroutine with
> 	could be declared like this:
> 			int TryIT(Ptr memoryAddress,long *value)
> 	the return value could indicate if the access was successful and
> 	the parameter value could returned the actual value read.
> 
> Question:
> 	Anybody has suggestions or better yet, code to do this ?
> 	Can it be done only in C ? I work with MPW 3.0 C and C++.
> 	( I hate assembler but I feel like this time I won't be able to
> 	avoid it &-)
> 	
> 	Thanks in advance,
> 		Louis
>;
Louis,
You need to find your controller's base address first, before you can
access it's registers.  Normally, you have a configuration rom on your
board with a ID number to identify it. Using the following, if
GetSlotBase returns 0, then your software should not try to access the
board.

sID		EQU	your_ID
------------------------------------------------------------------------------
; GetSlotBase
; 
; returns slotBase in D0, clear D0 if no card found
GetSlotBase	PROC
StackFrame	RECORD	{A6Link}
LocalSpBlock		DS	SpBlock
LocalSInfoRecord	DS	SInfoRecord
LocalSize	EQU	LocalSpBlock - *
A6Link		DS.L	1
Return		DS.L	1
		ENDR

	WITH	StackFrame,LocalSpBlock
	Link	A6,#LocalSize
	MOVEM.L	A0/A1/A4/D1/D2,-(SP)

	MOVEQ	#BeginSlot,D2				;;check slots in
reverse order (EI9)
nxt	CMPI	#EndSlot,D2				;;exhausted all
the slots?
	BGE.S	mor
	CLR.L	D0					; yes: return
nothing in D0
	JMP	Eop
mor	MOVE.B	D2,spSlot(A6)				; no: continue
searching next slot
	LEA	LocalSInfoRecord(A6),A1
	MOVE.L	A1,spResult(A6)
	LEA	LocalSpBlock(A6),A0
	_SReadInfo
	MOVE.B	D2,spSlot(A6)
	CLR.B	spId(A6)
	CLR.B	spExtDev(A6)
	MOVEQ	#1,D1
	MOVE.W	D1,spCategory(A6)
	CLR.W	spCType(A6)
	CLR.W	spDrvrSW(A6)
	CLR.W	spDrvrHW(A6)
	LEA	LocalSpBlock(A6),A0
	_SNextTypesRsrc
	MOVE.B	#32,spId(A6)
	LEA	LocalSpBlock(A6),A0
	_SReadWord
	LEA	spResult(A6),A4
	SUBI.W	#sId,2(A4)
	DBEQ	D2,nxt						; on
exit, D2 <- 0000000s

	MOVE.L	D2,D0						; D0 <-
0000000s
	LSL.W	#4,D0						; D0 <-
000000s0
	OR.B	D2,D0						; D0 <-
000000ss
	OR.W	#$F00,D0					; D0 <-
00000Fss
	LSL.W	#4,D0						; D0 <-
0000Fss0
	SWAP	D0
; D0 <- Fss00000
Eop	MOVEM.L	(SP)+,A0/A1/A4/D1/D2
	UNLK	A6
	RTS
	ENDWITH
; StackFrame,LocalSpBlock
	ENDPROC	;GetSlotBase

Hope this helps,
Steven Ting
Linotype Company