Re: [lwip-users] PPP with NO_SYS=1 in an interrupt context (Simon Goldschmidt)

[Iordan Neshev]

On 6/14/2011 1:30 PM, address@hidden wrote:
> Message: 2
> Date: Tue, 14 Jun 2011 13:17:38 +0200
> From: "Simon Goldschmidt"<address@hidden>
> To: Mailing list for lwIP users<address@hidden>
> Subject: Re: [lwip-users] PPP with NO_SYS=1 in an interrupt context
> Message-ID:<address@hidden>
> Content-Type: text/plain; charset="utf-8"
>
> "Mehmet Ali Ekici"<address@hidden>  wrote:
> > >  PPP with NO_SYS=1 in an interrupt context
> [snip]
> I think the PPP setup should be fine. As I'm really not a PPP expert, I can't 
> tell why you get a bad fcs. I remember getting this also sometimes, but Iordan 
> (who helped me with PPP bugfixes) said it might be due to me using a virtual 
> COM port... Maybe he can comment on this if he still reads this list...
>
> Simon
> -- Empfehlen Sie GMX DSL Ihren Freunden und Bekannten und wir belohnen 
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Once I did get the "Dropping bad fcs" error too often. It turned out 
that at the particular baud rate I was working  the bit error rate of 
symbols coming in and out of the UART was too high. In other words - 
these were frame errors.
UARTs (almost) never have 100% accuracy due to the discrete steps of the 
baud rate generator, which depend on the clock rate. I guess that the 
drifts of the MCU and the modem baud rates are in opposite directions.

First try all the possible baud rates through 9600 to 115200 bps and let 
us know if it helps. That should be easy.

Also check if your UART has flag for Frame Error. LPC2xxx MCUs have it. 
You must check it in the UART's Rx interrupt handler.

By the way, what exactly modem do you use? It might be related to 
another problem that I'll have to solve when I find the time.

Iordan