[Tinyos-devel] lost packets from PC to the mote

[Andreas Koepke]

Vlado Handziski:
> The msp430 has separate shifter and character buffer, so the time window is
> about 1.5-1.7 times larger.  

Wrong, see queueing theory.

 > And I believe Ben has tested that no overflows
> at the bottom-part of the ISR are causing this.

But long atomic blocks elsewhere may cause it.

> Vlado
> 
> On Mon, Apr 21, 2008 at 9:17 PM, Andreas Koepke <koepke at tkn.tu-berlin.de>
> wrote:
> 
>>>> Correct, now for a little math: At 115200 Bit/s the uC has 86us to
>>>> process each byte.
>>> 115200 bits = 14400 bytes and 1/14400 is about 7e-05. So the MCU has
>>> around 70us to deal with each byte.
>> Don't forget the start and the stop bit ;-)
>>
>>>> If both directions are used, this drops to 43us. Scheduling a timer
>>>> takes about this much in T2. So if the node happens to do something
>>>> else than mere byte crunching, packets may be lost.
>>> This situation should be indicated by some overflow register from
>>> MSP420, right?
>> The uC can signal this, but the default configuration in T2 prevents
>> this. So to check this, change the default configuration for the serial
>> interface and modify the interrupt handler (you have to check the flags
>> immediately before reading the byte).
>>
>> Best, Andreas
>>
>>
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>>
>