[En-Nut-Discussion] samples at 8kHz

[Christian Wieser]

Hello Harald et al,

we have done part "-B->" and "<-C-" successfully with native
interrupts, and can send out packets at the required pace. However,
calling NutUdpReceiveFrom takes around 80 to 100ms (on an Ethernut
2.1). 

Is there a way to decrease the execution time of this function?

We are also facing too long delays it we yield to another thread.

Cheers,

Christian


> Christian,
> 
> Well, I think in the first place it should be noted,
> that UDP isn't reliable. There will be no fixed "clock"
> for incoming or outgoing packets. Thus some buffering is
> required:
> 
> Ethernet -A-> InBuff -B-> DAC
> 
> Ethernet <-D- OutBuff <-C- ADC
> 
> The arrows may be viewed as tasks, reading from or writing
> to buffers.
> 
> Tasks B and C must be strictly time controlled, best
> using a native timer interrupt. Nut/OS uses timer 0 only.
> For example, timer 1 can be used:
> 
> SIGNAL(SIG_OUTPUT_COMPARE1A)
> {
>      outb(TCNT1H, 0);
>      outb(TCNT1L, 0);
>      /* DAC or ADC work here */
> }
> 
> /* Timer initialization, see ATmega128 datasheet. */
> void InitTimer1(void)
> {
>      NutEnterCritical();
> 
>      outb(TCCR1A, 0);
>      outb(TCCR1B, _BV(CS12));
> 
>      outb(TCNT1H, 0);
>      outb(TCNT1L, 0);
>      outb(OCR1AH, 0x01);
>      outb(OCR1AL, 0x00);
> 
>      sbi(TIMSK, OCIE1A);
>      NutExitCritical();
> }
> 
> However, interrupt latency might be too high to maintain
> ADC/DAC frequency. Thus, extra hardware may be required.
> 
> Tasks A and D are simple threads. Note, that it is impossible
> to have UDP packets at exactly every 20 ms. Ethernet is non-
> deterministic. Even switched Ethernets got some jitter, at least
> caused by the CPU in the switching hardware.
> 
> Harald
> 
> At 16:55 14.10.2004 +0300, you wrote:
> >Hello,
> >
> >I am not sure how to realize the following thing - a simple IP
> >telephone. I have realized the Control Plane by adopting a simplified
> >form of SIP (Session Initialization Protocol)
> >
> >But I come into troubles realizing the Media exchange.
> >
> >The phone should sample voice from ADC0 and makes out of it an RTP
> >(Real Time Protocol) Stream (using G.711 encoding I have to send a UDP
> >packet every 20ms). I have to get a sample every 125us (8kHz) and kick
> >incoming RTP packets piece by piece to an PWM counter.
> >
> >My question now is: Can this be done using NUT/OS? What would be a way
> >to do so?
> >
> >Cheers for any answers,
> >
> >Christian Wieser
> >mailto:chwieser at ee.oulu.fi
> >
> >
> >_______________________________________________
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> 
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Christian Wieser
mailto:chwieser at ee.oulu.fi