🚀 go-pugleaf

In article <4793@leadsv.UUCP> ereed@leadsv.UUCP (Ed Reed) writes:
>
>
>I am having a problem with the FSRead command on a Macintosh II. The
>problem is as follows:
>
>I have three processors, the Mac II, a Force single board computer, and a high
>speed processor board.  The Force is the traffic cop of the system. When the
>system is running the HSP sends data to a register which the Force reads. The
>Force then takes that data and sends it to the Mac II. The problem is in order
>to maintain a realtime system, the Force sends a byte of data to the Mac II 
>every iteration of the control loop. Now FSRead appears to be only getting part
>of the data. In a test case 0 to 255 was sent from the Force to the Mac II, and
>approximately every 3rd byte was read. The other bytes where zeroed. Any
>suggestions. The actual Mac code is:
>
>FSRead (InPort, 256, &DataIn);
>
>and was written in C using Lightspeed C ver 3.0.
>
>Please reply to Joe Hughes
>
>Joe Hughes
>pyramid!leadsv!jhughes

Ack!!  and double Ack!!

Read Inside Mac carefully!  I have used this routine so many times that
I always do the code the same way:

foo(InPort, DataIn)
int InPort;
Ptr DataIn;
{
	OSErr err;
	long bytes_to_read;

	bytes_to_read=256;
	err=FSRead(InPort, &bytes_to_read, DataIn);
	return(err);
}

The problem with your code is that you aren't passing a pointer
to the number of bytes to read.  Inside Mac Volume II-92:

	FSRead(refNum: INTEGER; VAR count: LONGINT; buf: Ptr);

In C, one should always interpret a VAR as meaning requiring '&'.

I hope this helps.

Patrick Beard
Lawrence Berkeley Laboratory