[Simh] Way out idea for simh

[Johnny Billquist]

On 2016-04-20 22:35, Sampsa Laine wrote:
>
>> On 20 Apr 2016, at 23:25, Phil Budne <phil at ultimate.com> wrote:
>>
>> Ken.Cornetet wrote:
>>> I guess I need to shout this:
>>> ******* KERMIT DOES NOT WORK ON SIMH EMULATED RTE-6/VM ********
>>
>> Why not?
>>
>>> Kermit does not exist (and probably couldn't feasibly exist) on any earlier versions of RTE.
>>
>> Again, why not?
>>
>> Having just written a new shell for PDP-7 UNIX (because the original
>> could not be found), I can't imagine much other than a lack of
>> something resembling a serial console that would prevent _some_
>> version/subset of KERMIT (or something similar like X or ZMODEM) from
>> being cobbled together.
>>
>
> And since the connection can be assumed to be lossless, the protocol could be really simple, e.g. something like this:

Actually, we should not assume the connection is lossless, so I would 
stick with Kermit.

(There are examples of overflowing the serial port, resulting in lost 
characters by simple buffer overruns.)

> G=Guest, H=Host
>
> Example of a write operation..
>
> G:	WRITE-FILE
> H:	ACK
> // Now we send the file structure / word size etc
> G:	FILE-META-DATA
> G:	<file size and a bunch of OS specific stuff that is written to a second file>
> H:	ACK
> G:	FILE-DATA
> G:	<the actual data>
> G:	ACK

Add checksums to the packets, and this is pretty much what Kermit is.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol