Path: utzoo!utgpu!water!watmath!clyde!bellcore!tness7!killer!elg From: elg@killer.UUCP (Eric Green) Newsgroups: comp.sys.cbm Subject: Re: Burst Mode on C-64 ? Message-ID: <4376@killer.UUCP> Date: 7 Jun 88 02:08:06 GMT References: <1988Jun5.024514.28021@ziebmef.uucp> Distribution: na Organization: The Unix(R) Connection, Dallas, Texas Lines: 32 in article <1988Jun5.024514.28021@ziebmef.uucp>, ross@ziebmef.uucp (Ross Ridge) says: > In article <4241@killer.UUCP> elg@killer.UUCP (Eric Green) writes: >>in article <1988May27.175829.5648@ziebmef.uucp>, ross@ziebmef.uucp (Ross Ridge) says: >>Note that bit-rate for each byte during burst mode is 250,000 baud, not 4800 >>baud. Burst mode is FAST. With the 1581, which reads data off disk at a >>reasonable rate, the 128 is almost as useful as a real computer. >> > 250 000 baud? That's almost 32k a sec. and as I understand it burst mode is > only slightly faster than improved serial bus the 128/1571 uses. Hmm... The BIT rate is 250,000 baud (the fast-mode routines shove a "4" into the timer which provides the shift-register clock). Actual throughput is much less, because between each byte, a sizable amount of time must be spent handshaking. However, because the disk drive shoves data out its serial port at that bit rate, you must still be capable of reading a single byte of data at that bit rate. The 6526's serial shift register can do that. Your software never will. As for the speed of burst mode: It is considerably faster than "fast mode", because it has much less handshaking overhead. For example, one test I did was loading Nezterm (a 200-block file). Took about 20 seconds in fast-mode. Took 8 seconds in burst mode. Try it yourself. Write a tight, clean assembly-language program which does nothing but read bytes from the file, in fast-mode. Then do a burst-mode load. The principle is the same (all that the "load" routine does, in the absense of burst mode, is read bytes from the file one-at-a-time and shove'em into RAM). -- Eric Lee Green ..!{ames,att,decwrl,ihnp4,mit-eddie,osu-cis}!killer!elg Snail Mail P.O. Box 92191 Lafayette, LA 70509 "Is a dream a lie if it don't come true, or is it something worse?"