First, I know I was a little overboard on the "RS232 is dead" theme, there are still uses for it, and it remains useful for its purpose.
However, the time when *everything* had rs232 available has passed now, and it was that which made it attractive as an alternative console (boosted by many older systems having no other console than an rs232 interface) It seems to me that we need something now to replace it (or to act as an alternative - rs232 consoles will still exist for systems that require or even just permit them of course) - something that can be depended upon existing (almost) everywhere (that is relevant anyway). To me, USB seemed to be the obvious candidate, as USB ports exist on just about everything now, as RS232 did in the past. But ... Joerg Sonnenberger <jo...@britannica.bec.de> said: | You don't need "just" a cable, but one with quite a bit logic in between. | USB is not designed for host-to-host communication, Thanks - that's the kind of info I was lacking, given I know nothing about USB... I had naively assumed that something which calls itself a universal serial bus would actually have some of the characteristics that would justify such a name. I was kind of anticipating there might be issues with USB power, but I had a vague understanding that it might be possible to control that. Michael van Elst <mlel...@serpens.de> said: | There are such "cables", That would kind of defeat the purpose, of allowing a connection to be made, simply, without needing anything particularly special. But I guess something like that might be better than nothing. | Then you have USB OTG [...] Often used in ARM systems [...] | We don't support OTG. Also might be useful I guess, perhaps allowing one of those small systems to act as a console for any other system being debugged, but again, not really very general. Lack of support (currently) isn't necessarily a problem, none of this currently has any support - any of it would require lots of code to be written. Mayuresh <mayur...@acm.org> said: | Even nicer if such device could be a smartphone, That's looking like perhaps a better choice - phones are already "devices" rather than hosts aren't they? And they are almost as common as USB, so requiring that would not be overly limiting. Of course, I have no idea whether it is possible on those systems to get low level enough access to implement something like this. Michael van Elst <mlel...@serpens.de> said: | On the other side, USB as a low-level console is pretty limited. It requires | a complex software stack to work. That isn't necessarily a problem. It sounds impossible, but with enough restrictions on what needs to actually function, it might be achieved without too much hassle. Long long ago I did an implementation of config code (more or less a console) for a device that had nothing but ethernet. For that (and to avoid the issue that would arise here, of needing specialised client code) I used telnet over TCP. Sounds like a complex software stack, but wasn't really. The TCP and telnet implementations were (I believe) fully standards compliant, but were extremely limited. The Telnet would refuse all option negotiation for example, and refuse to operate any way but how it wanted (legal, but not generally useful). The TCP IP and ethernet were all polled, lockstep implementations (I send, you reply, one packet at a time). That achieved by simply setting the window size for receive very low - whatever size packets the other end transmitted, became the window size... Not useful in general, and definitely not efficient in any sense, but worked just fine for the purpose (only a single connection at a time of course.) The whole implementation turned out to be surprisingly small. Whether any of that kind of thing would be useful for a USB implementation I don't know. I do think we need to be looking for something better than "photo of the screen" for debugging very early problems - especially as that's a one way transfer, no way to enter "bt" or "p/x 0xffff00000eeee0" or something from a camera. I am convinced that RS232 is no longer suitable, I was hoping USB might be used as a replacement, but if not that, anyone have any ideas on an alternative (a few years ago I might have suggested ethernet, but wired ports are no longer endemic, and wireless does look to be too complex for this kind of purpose.) kre
