[En-Nut-Discussion] Ethernut newbie with a lot of questions

Sat Apr 22 18:26:26 CEST 2006

Thank you for the answers.  There are just a couple of things I would
like to clarify.  My hub vs. switch question.  The reason I asked this
was because one of the devices would be an ethernet camera which would
generate a lot of traffic I'd like to keep away from the ethernut board.
The radios I would be using would have a throughput of sub-500Kbps, if
ethernut can handle this then a hub it will be.  "then Ethernut 1 will
become quite busy."  Is this to say that ethernut 2 can handle the
traffic better?

I think you misunderstood my question about reading files.  As I
understand it NutHttpProccessRequest() automatically selects the
appropriate file and sends it out.  I am just wondering if there is a
way I can send files out manually.  I.e. not using
NutHttpProccessRequest().

Thanks again,

Greg Wood

-----Original Message-----
From: en-nut-discussion-bounces at egnite.de
[mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of Harald Kipp
Sent: April 22, 2006 4:05 AM
To: Ethernut User Chat (English)
Subject: Re: [En-Nut-Discussion] Ethernut newbie with a lot of questions

Hello Greg,

At 22:39 21.04.2006 -0600, you wrote:
>The work I have done has left me with more questions than
>when I started.

Obviously. The reply will result in a kind of FAQ. :-)

>
>Assuming the ethernut board is run behind a switch and not a hub how 
>much processor load does the stack and OS exert?  Suppose that a simple

>web server and maybe a telnet session are running.  Is there a time 
>limit that should be observed when a thread is blocking?  What is 
>reasonable number of simultaneous connected sockets?

As long as no packet arrives or has to be sent, the
processor load is 0%. When a packet is handled, incoming
or outgoing, the load is 100%. Sorry, I didn't want to
make fun of this. But the question can't be answered easily, because it
depends on the application code. The CPU is running at 100% all the
time, either in idle thread, system or application code.

Most Ethernet Drivers use a timeout while waiting for incoming data.
This is a safety feature to detect crashed Ethernet Controllers. The
load is probably far below 1%.

If you want a time limit while waiting, you can set the
read timeout socket option.

The number of simultaneous connections is limited by available RAM,
which again depends on your application code.

>
>What are the consequences if ethernut is run behind a hub and not a 
>switch?

When connected to a HUB, Ethernut has to handle all broadcasts of that
segment. Depending on the number of connected nodes and the type of
services, this may indeed put a noticeable load on Ethernut. Let me say
it the other way. If 200 kBytes are broadcasted every second, then
Ethernut 1 will become quite busy.

There had been several reports during the last weeks, that Nut/OS fails
when connected to large networks. But there is no logged incident and
all test to simulate this were negative.

>
>What is the best way to implement ISRs?  I'm done a lot of programming 
>with WINAVR, can I still use SIGNAL functions?  Are there any special 
>considerations when doing this?  Is there any new delays created in 
>responding to an ISR from the OS/stack?

You can use native interrupts without limitation, except Nut/OS for AVR
uses timer 0 as it's system timer.

There are several delays caused by critical sections, where Nut/OS
disables interrupts. This topic has been discussed in this group to some
extends. There is still potential for minimizing these sections.

>
>Are the streaming functions, specifically printf, interrupt based when 
>used with the uart?

Depends on the UART driver you use. devDebug is a polling driver, which
allows you to use streaming functions in interrupt context. devUsartAvr
is fully interrupt driven, including hardware handshake and half duplex
control.

>
>I'm somewhat new to real time OSes.  Can someone point me to a good 
>source if information about programming with Nut/OS?  I've read the 
>ethernut software manual and it left me wanting more.  The nut/API 
>reference does not have sufficient explanation for some things to make 
>sense to me.  I'd like to see some example programs that take advantage

>of some of the features availabe in Nut/Os.  In the past I've used 
>global variables to pass info in and out of ISRs, what is the prefered 
>method to do this in Nut/Os?

The app directory contains a number of examples. Most developers study
the Nut/OS source code to see how things are done. There is also book,
but this requires that you can ready Chinese. :-) Seriously, we are
constantly working on this matter.

>
>I've got an application in mind in which several ethernet devices will 
>exist on a robot and be connected via an ethernet radio to a LAN.  I'd 
>like to have the oem radio module mounted atop my electronics which 
>will likely be an ethernut compatible setup.  I want to avoid having to

>go
>radio->magnetics->switch<-magenets<-ethernut.  It seems to me that if
>everything will be build onto a PCB there is no need for magnetics.  Is

>there a chipset that implements a simple 4 or 5 port 10mbps switch that

>would allow me to avoid the magnetics for the devices that are on the 
>pcb together, and also build the switch onto the PCB?

On a local segment like this there is no need to worry about the load
caused by broadcasts. Thus a HUB will be just fine. May be someone else
can answer the electrical part, but the transformer build into Ethernut
1.3 also contains the filter. On some other controller chips this filter
is build in.

>
>Is there some software out there that will allow me to send information

>to specific IPs/ports via TCP and/or UDP?  Basically the equivalent of 
>a serial terminal program that supports binary data.  For serial 
>applications I've used windmill and brays terminal.

For TCP there probably are, for UDP probably not. I prefer
to write my own, adapted to the specific application. There's nothing
magic.

>
>Is it possible to port ethernut over to other members of the AVR family

>such as the new fangled 100 pin devices?

If you know a compiler which can generate code for these devices. The
main problem with Nut/OS is, that function pointers are 2 bytes, while
the ATmega2560 requires 3 bytes. Similar problems with the stack.

>
>Is there a way to manually read/send files from urom.c?  I wrote a 
>simple CGI and it seems to me like it would be nice if you could just 
>send out a file to fill in parts of a CGI page.

No, UROM is read-only. PNUT is volatile and PHAT is only available for
Ethernut 3 right now.

>
>I'd like to see some ethernut applications.  If someone could post some

>links to ethernut based projects that would be great.

http://www.ethernut.de/en/community/appliances.html
but mostly commercial.

A few others published some code, you may google for it.

For example:
http://www.usbdip.de/

>
>Anyone written a DNP3 driver for ethernut?

Not that I know of.

>
>Anyone interfaced an ethernut 1.3 board to a SD/MMC card?  How about 
>other storage devices?

I've heard about MMC, but nothing had been finally documented.

Again Michael's page might be interesting
http://www.usbdip.de/

http://www.ethernut.de/en/medianut/index.html
The picture at the end of the page shows Datanut with
CF and IDE.

>
>How about an ethernet based bootloader?  Ponyprog is painfully slow. 
>How can I use my STK500 compatible programmer with my ethernut board?

When you bought Ethernut, it contained a pre-loaded bootloader. eboot is
available here http://www.ethernut.de/en/hardware/enut1/index.html

>
>Can Nut/Os be run on a stripped down system?  I.e. just the ATMEGA128? 
>I'm thinking at least the external SRAM is required.

Yes, we use this in commercial applications. Of course, no TCP/IP.

>
>Sorry for all the questions.  I'm sure some of them are answered within

>the ethernut documentation.  If you can refer me to certain documents 
>thats great.  I've got a lot to learn about ethernut and ethernet and 
>have gotten a little tired of reading and searching for information the

>last 3 days.

You're welcome. As long as this doesn't happen once a day,
it's OK to answer a couple of questions in one go. It's helpful for
others as well, who may have similar questions.

The answer might have been even faster, if you wouldn't have used HTML
formatting. The total size of your message was beyond the 10k limit and
the admit (me) had to manually confirm it. More info is here
http://mailformat.dan.info/body/html.html

Harald

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