From: Jim Brain (brain_at_jbrain.com)
Date: 2004-05-27 09:31:26
>I see, you would prefer to have clean layers in the protocol. Instead of >escaping of 00 payload bytes, you would like to escape 00 bytes also in the >parameters of commands. I don't know what you would achieve with that. >Of course, there must be a resynchronization mechanism, in case of >intermittent communications failure. I'm using the BREAK condition as a >signal to reset the microcontroller to idle state. > > If the system gets too far out of whack, command data could get misinterpreted as a command code (in your example, 00 LISTEN 00 00 00 00 FF (32 bits) coudl get mangled into 00 LISTEN 00 00 00 00 CMD_FF (whatever this is). At least with escaped command data, sync issues are less of an issue. Minor nit. >I didn't consider that, because I have the feeling that the serial bus is >slower than the 38400 bps line. Most executable programs for the >Commodore 64 have been compressed, and there are no long sequences of zero >bytes. I picked zero as the escape byte, because testing against zero is >easy on the AVR. Testing against some other constant requires that the >value is loaded to one of the registers 16..31. > > True, but I tried FF, and I got into issues where the system might get off a byte (bad code), and then it gets worse. FF FE or F2 02 or something worked much better. I know 00 is easy, but 00 just shows up so much, In some files, it could double the size of the file. >I would like to make it possible to upgrade existing C2N232 units, and to >save trouble in circuit board design. You're right, there's no need to >stick to a smaller controller. But I like challenges, and I'm not yet >hitting the limits of the 2313 too hard. (Are you familiar of Levente >Hársfalvi's RS-232 to 1351 mouse adapter done with a PIC? That's a real >challenge.) > > Well, I think some standardization on protocol might be useful. >10 years ago, I was dreaming of something similar: a programmable device >for the serial bus. Currently available microcontrollers are making the >dream possible at an affordable cost. > > As was I, but I dind;t have the tools or the expertise to do it. Now, I have both. >>I could try. I was waiting a bit until I put the JDos routines in >>before I laid out the diagram in a package, to make sure I actually >>capture all of the relevant states. >> >> > >It'd be good to draw one diagram without JDos and another including it. > > That was the plan, but have them as overlays. >What does ?ST say after such a failed LOAD attempt? > > 66 (with my code, not sure on base 64) >I don't think that there is EOI handshake for bytes sent under ATN. >I concluded this after reading the VIC-20 KERNAL routines. Come to >think of it, EOI handshaking for ATN would make things very complicated >when you're talking to multiple devices. And there is no EOI handshaking >for the first ATN byte, is there? > > I am getting the impression that EOI is never used when ATN low. As stated in another email, I have server code running. save "/home/brain/incoming/stuff",13 is working Load needs a bit more thought. It works now (I have a hardcoded app stored on the AVR for testing), but I need some commands to send to the AVR to tell it to wait for data, or not to bother, because file cannot be found. JIm -- Jim Brain, Brain Innovations firstname.lastname@example.org http://www.jbrain.com Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times! Message was sent through the cbm-hackers mailing list
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