Losing characters in serial communication

[Jason Lemm]

Hi.
I am trying to develop an application as part of an assignment.
The assignment requires that we use the serial compatibility mode (and
we have a stripped down serial link with no hardware handshaking).

The problem I have is quite straight forward.
One computer builds a string (a packet) and sends it byte by byte over
the serial line.
The other computer sits in a while loop, and waits for a special
character to signify the start of a string... (it is looking for a
"["). When it sees this, it moves to the next frame of a sequence,
and reads byte by byte appending to a string, until it sees the end
character (which is a "]").

If I run the receving end in highlight execution mode, everything
works as expected. If however,
I run the programs in normal mode, I
lose random characters from the start of the string..

So if I should receive "[a1:b1:test]" I might only receive "[:test]".

Can anyone suggest why this is happening, or another possible solution
which wont have this problem.

I have tried putting a 100ms delay in each loop, which seems to solve
this problem, but a 100ms delay is not acceptable for the purpose of
this application.

I am not asking for help completing the assignment, I am merely stuck
with this issue and cant continue until this problem is solved.

Any help is greatly appreciated,

Jason

[waldemar.hersacher]

Hi Jason,

I haven't got the experience losing characters. But I do use a wait in the while loop. Most I use 10 milliseconds. I use "Bytes at serial Port" to get the number of bytes in the buffer. Then I read the buffer and concatenate the strings together. With the string functions I search for the delimiting characters. If I have found them I will remove the desired string. The rest of the string is holded in a shift register until the next packet is to extract.

This has a maximum delay of one wait.

So change your algorithm from byte by byte operation to string operation.

Waldemar.

[ummagumma]

i have run into problems losing characters by having a read routine that clears the input buffer first. ie... my routine would:

-get number of bytes available
-read that number of bytes from port (but not save the output)
-send a command if one needed to be sent
-wait for characters to store/return, looking for a cr or end of line (or timing out)

this routine, when called in a loop, loses characters because the first few are erased. the routine was designed to clear the input buffer, send a command, then wait for a response. when using it oustide of that functionality to just wait for a response, it erased available bytes when starting.

this doesn't sound like your problem but perhaps some added insight.

[Ben]

HI Jason,

Others have tried but I see no winners yet.

Post your code and someone will take a look.

I am much better with visual aides.

Ben