Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!faatcrl!jprad From: jprad@faatcrl.UUCP (Jack Radigan) Newsgroups: comp.sys.amiga Subject: Re: USR 14400/V42bs and Amiga Message-ID: <655@faatcrl.UUCP> Date: 2 Jan 91 00:53:23 GMT References: Organization: FAA Technical Center, Atlantic City NJ Lines: 42 torkell@ifi.uio.no (Torkel Lodberg) writes: >In a message, Matti Joutkoski writes: >>JR-Comm is truely lazy, and hard load to the Amiga. It have problems >>with 38400. >Well you can't really blame Jr-Comm. As a matter of fact, it has a very >quick Zmodem transfer protocol that should stick with much faster >transfer speeds than 38400 baud. The real problem is the Amiga system >and the serial.device. Exact-a-mundo! The problem is due to the internal port not having the ability to buffer multiple bytes, it only buffers the most recently received byte. Add to this the fact that the serial port is addressed in chip ram space and that the cpu has the lowest DMA priority, and you have the added problem of the cpu being locked out while higher priority DMA is taking place. That's why I don't recommend 8 and 16 color screens at 19.2kbps, much less 38.4kbps. Finally, we have the problem of the cpu servicing the serial port interrupt itself. Although the cpu can normally service it with little problem, there are occasions when the cpu is delayed long enough so that the buffered byte is overwritten by the next incoming byte. The most common situations that I've seen cause this are more than two floppy drives and/or hard disk partitions being mounted. AmigaDOS is evidently doing a Disable() long enough to cause data loss when it checks each device for a disk change. Another cause is having a task with a excessively high task priority, usuallyt above 15. >I guess the Amiga would have been better suited for fast transfers >if CTS/RTS would had been properly handled by hardware. 38400 >baud works pretty well on the A3000 (due to the more powerful CPU) >but it is still irritating that data may disappear during a transfer. >Especially this makes it very unsafe to use a protocol like Ymodem-G. Yes, the A3000 and any A2000 w/3rd party serial cards run 38.4kbps without problems. If C= decides on a new Paula chip I hope multiple byte buffering finds its way in there... -jack-