Re: Serial issue

[Mark Hounschell <markh@compro.net>]

linux-os (Dick Johnson) wrote:
> On Fri, 18 Aug 2006, Lee Revell wrote:
> 
>> On Fri, 2006-08-18 at 15:15 -0400, linux-os (Dick Johnson) wrote:
>>> A file-transfer protocol??? Has he got hardware the __required__
>>> hardware flow-control enabled on both ends? One can't spew
>>> high-speed serial data out forever without a hardware handshake.
>>>
>> Interesting you should mention that.  As a matter of fact I have to
>> disable all flow control or the serial console doesn't even work.  I
>> considered this a minor issue and had forgotten about it.
>>
>> But, in polled mode with no flow control I can transfer a 10MB file.
>> There are a lot of retransmits but it works.
>>
>> Lee
>>
> 
> Using RS-232C for file transfer and as a serial console are two
> different things. Many terminals and terminal emulators don't
> even activate RTS/CTS. If you are just getting data from the
> output of a UART to view on a screen, the data usually comes
> in spurts, a line at a time, and a screen at a time. There
> is plenty of time for the receiving terminal to write the
> stuff to the screen.
> 
> However, with file transfers, data streams with no breaks.
> There needs to be time for these buffers of data to be written
> to files, etc., or else you eventually run out of buffers even
> if no interrupts are ever lost. Therefore, you must use hardware
> handshake. In other words, you need to connect your machines
> together with a complete null-modem cable, not just three wires.
> Then both machines need to cooperate, i.e., the receiving machine
> needs to lower CTS before its buffers get full and the sender,
> must look at its RTS bit and wait for it to go false before
> sending anymore data. Failure to do this __will__ result in
> lost data.
> 

Don't mean to but it but:

Take it from someone who actually still uses dumb terminals every day, any thing
over 9600 baud still requires some kind of flow control for reliable consistent
operation. Software (Xon/Xoff) and or hardware (RTS/RTS/DTE) flow control.


Mark