Re: [Bacnet-developers] MSTP on Linux - is it ever possible?

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Thanks Vasu Vallabhaneni!!!

It worked.

--- On Fri, 4/2/11, Vasu Vallabhaneni <vas...@hc...> wrote:

From: Vasu Vallabhaneni <vas...@hc...>
Subject: Re: [Bacnet-developers] MSTP on Linux - is it ever possible?
To: "Discussion for developers of the BACnet stack" <bac...@li...>
Date: Friday, 4 February, 2011, 7:54 AM

Hi
        Buddy. You said that the BACNET_MSTP_MAC=0x6F. We need two different MAC addresses too. So take two terminals set two different MAC addresses for env variables.and try it.

Ex:- export BACNET_MSTP_MAC=0x6F. In one terminal.
     export BACNET_MSTP_MAC=0x01. In other terminal.
I hope that it will work.

Regards
Vasu Vallabhaneni
HCL Technologies Ltd.
Chennai - AMB1, D12&12B,
Ambattur Indl.Estate, Chennai 600058 (India)
Tel: +91-044-26230711 Extn: 2208
cell:9566088955
vas...@hc...
-----Original Message-----
From: Kåre Särs [mailto:kar...@wa...]
Sent: Friday, February 04, 2011 12:37 PM
To: spo...@em...; Discussion for developers of the BACnet stack
Subject: Re: [Bacnet-developers] MSTP on Linux - is it ever possible?

Hi,

On Thursday 03 February 2011 18:49:43 Sergei Poselenov wrote:
> Hello all,
>
> I'm trying to test the bacnet-stack MSTP basic functionality, which I
> have built on Linux x86, version 0.5.7.
>
> I have two serials on my PC, connected via a null-modem cable.
>
> I ran:
> BACNET_MSTP_BAUD=115200 BACNET_IFACE=/dev/ttyS0 ./bin/bacwi 260001
> and
> BACNET_MSTP_BAUD=115200 BACNET_MSTP_MAC=0x6F BACNET_IFACE=/dev/ttyS1
> ./bin/bacserv
>
> ... and got nothing.
>
> I also tried to enable hardware flow control, and ran both programs
> under "ionice", as suggested in ports/linux/rs485.c, without much
> success.
> I only had success when I set:
>
> static uint8_t Treply_timeout = 26000;
> static uint8_t Tusage_timeout = 5000;
>
> I found a discussion of the Linux MSTP issue here
> http://sourceforge.net/mailarchive/message.php?msg_id=26633681
>
> Essentially, Steve is saying here that Linux is not fast enough to
> meet the strict MSTP timings.
>
> Could someone please explain (I'm sorry if I'm a hundredth who is
> asking) why is my 2.4 GHz P4 is not fast enough?
The problem is that a standard desktop Linux kernel is not a real-time kernel
and does not guarantee that you get millisecond timing. The kernel tick has
been 10 ms which means that if you call usleep() to sleep 1ms the thread will
sleap for at least 1 ms but might sleep up to 10ms. If you also have a broken
driver somewhere you might get up to 100ms sleeps even if you just asked for
1.

>
> Is it ever possible to use the the MSTP bacnet-stack configuration for
> implementing BACNet over RS-485 between two Linux-driven machines?
Most distributions do have a "real-time" kernel that improves the
responsiveness, but I'm not sure how accurate timing they have achieved. The
kernel tick can also be modified while compiling the kernel, but a shorter
tick will decrease the performance as there will be a lot of extra context
switches.

I have been running an MSTP stack on linux to debug an MSTP device, so it is
possible to communicate, but the reliability of the communication is not
guaranteed to work 100%

>
> And why is BACNet IP implementation works fine on two PCs?
BACNet IP does not have the same strict timing requirements.

/Kåre

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------------------------------------------------------------------------------
The modern datacenter depends on network connectivity to access resources
and provide services. The best practices for maximizing a physical server's
connectivity to a physical network are well understood - see how these
rules translate into the virtual world? 
http://p.sf.net/sfu/oracle-sfdevnlfb
_______________________________________________
BACnet-developers mailing list
BAC...@li...
https://lists.sourceforge.net/lists/listinfo/bacnet-developers