Path: utzoo!utgpu!water!watmath!clyde!rutgers!psuvax1!vu-vlsi!cbmvax!fred
From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: Random files problem w/sprites enabled on C64
Message-ID: <3166@cbmvax.UUCP>
Date: 19 Jan 88 19:59:48 GMT
References: <1293@edison.GE.COM>
Organization: Commodore Technology, West Chester, PA
Lines: 55

In article <1293@edison.GE.COM>, mfs@edison.GE.COM (Martin Sant) writes:
> Over the weekend I was pulling out my hair over a strange quirk I
> discovered while using random files on my C-64/FSD setup.  I found
> that the computer would 'hang-up' if I tried to use the 'b-p:'
> command while I had sprites enabled...
> After I disabled the sprites, things worked fine...
> 1) Why does this happen ?

	The serial bus timing (slow or fast) is critical.  Enabled sprites
	cause the VIC to kick the processor off the bus longer than usual
	at "random" times (depending upon the placement of spites on the
	screen) in order to fetch sprite display data.  Should this
	inordinately long VIC DMA occur during sensitive timing operations
	(or even edge-sensitive triggers) the system will not work right.
	This is rather well known, at least among old time hackers and
	developers.  For this reason, the C128 kernel temporarily disables
	sprites during critical timing loops.

> 2) Is it particular to the FSD or does the 1541 do this too ?

	It does not have anything to do with the drive- it is a problem
	on the host side.

> 3) Random files in general; I can use all of the sectors on the disk
>    can't I ?  I don't need to store any 'real' DOS files. Can I write
>    over the sectors where the directory, etc. are stored ?  Is there
>    a difference between the ua:/ub: and the u1:/ub commands?

	Technically you can use the entire disk, system sectors and
	all, but I would recommend against it- it would be difficult to
	manage, backup, etc. without a functioning directory.  If you
	need more room, perhaps the 1571 (340K) or 1581 (790K) drives
	would suit your application better.

	There is no difference between U1 and UA commands; the DOS simply
	ANDs both of them with $0F to form an index into the user function
	dispatch table.

> 4) The JIFFY DOS stuff that was mentioned on the net several weeks 
>    ago:  Does it work ok with random files ?

	Sorry, I did not see that posting.  The RAMdisk does not support
	direct access commands such as these, but it does support REL
	files.

> Mar Tan 
> GE Fanuc Automation 
> Charlottesville, VA 22901
--
-- 
Fred Bowen			uucp:	{ihnp4|rutgers|caip}!cbmvax!fred
				arpa:	cbmvax!fred@RUTGERS.EDU
				tele:	215 431-9100

Commodore Electronics, Ltd.,  1200 Wilson Drive,  West Chester,  PA,  19380