oster@lapis.berkeley.edu (David Phillip Oster) (08/18/86)
In article <855@usl.UUCP> elg@usl.UUCP (Eric Lee Green) writes: >A Macintosh won't run at 19200 baud. To scroll the screen, it needs to >move 32K of RAM. I would estimate it takes at least 20 clock cycles >per word to move it, which would be roughly 320,000 clock cycles for... The actual figures are: Ram, maximum of 22k screen ram. 10 clock cycles per word (use MOVEM instructions: @1 MOVEM (a0)+,a2-a6/d1-d7 ;64 clock MOVEM a2-a6/d1-d7,(a1)+ ;64 clocks DBF d0,@1 ;10 clocks = 138 clocks to move 54 bytes = 55936 to move the whole screen, almost 6 times faster than Eric Green calculated, and plenty fast enough to keep up at 19200. In fact, one of the design goals of the mac was that it be fast enough to simultaneously write to the floppy, read characters at 19200, and display them on the screen! --- David Phillip Oster -- "The goal of Computer Science is to Arpa: oster@lapis.berkeley.edu -- build something that will last at Uucp: ucbvax!ucblapis!oster -- least until we've finished building it."
b-davis@utah-cs.UUCP (Brad Davis) (08/19/86)
In article <1108@jade.BERKELEY.EDU> oster@lapis.berkeley.edu.UUCP (David Phillip Oster) writes: >In fact, one of the design goals of the mac was that >it be fast enough to simultaneously write to the floppy, read characters >at 19200, and display them on the screen! Of course this was done by slowing the floppy down to the point that no one would want to write the floppy while doing anything else. -- Brad Davis {ihnp4, decvax, seismo}!utah-cs!b-davis b-davis@utah-cs.ARPA One drunk driver can ruin your whole day.
milo@ndmath.uucp (Greg Corson) (08/20/86)
I have been working on a terminal program for the Mac designed to operate at 9600 baud and above. I can offer some real-world figures on how fast the Mac can actually display characters...these figures are based on benchmarks on my own code. Special case scroll of 85x24 screen 1.07 ticks (A tick is 1/60th of a second) Character drawing (my code) over 4000 characters per second With these speeds it is farely easy to put together a 19200 baud terminal program that requires little to no handshaking. I have a prototype of my program running now. I have been using it connected to a Unix box over a 19200 baud serial line. So far, in normal use, NO handshaking has been required, in fact it has never even come close to needing handshaking. The program has a 4k serial buffer allocated and the most the buffer has ever backed up is about 150 characters. I'm sure if you fed the program 4000 line feeds in a row it would eventually need to use the handshaking, but this is very unlikely to ever happen in real life. With a 4000 character per second drawing rate the program quickly catches up with any scroll induced delays. I will soon be releasing a version of this program as shareware, the first version will probably emulate a DEC VT52---later versions may emulate more complicated terminals...I chose the VT52 for the first version because it is easy to do. That way I can get the program released sooner. If you are interested in getting this program please send me mail, the more support I get from people on the net, the quicker I will get the program finished. Greg Corson pur-ee!iuvax!kangaro!milo