I looked at the ppp chat source and it uses putchar to write to the device. When PPP is run over a line discipline like n_gsm, which multiplexes a tty via the GSM 07.10 protocol, a lot of extra data is created on the link.

Can I use stty or some other feature to glob data together? For example, if the chat script has AT\n, the following may be sent to the serial port (with n_gsm),

f9 07 ef 03 41 d4 f9  ....A..
f9 07 ef 03 54 d4 f9  ....T..
f9 07 ef 03 0d d4 f9  .......

The extra characters are the n_gsm framing to a particular virtual serial port. I would prefer,

f9 07 ef 07 41 54 0d xx f9  ....AT...

Reducing the traffic from 21 characters to 9 (and I haven't included acknowledgements). The AT GPRS question has some information related to this question.

What I am asking could also be achieve by altering ppp's chat to use strchr('\') and using write() instead of putchar. I am hoping there is some stty command turn on a Nagle like algorithm for a TTY.

07.10 standard

n_gsm docs


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