Subject:
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Re: LegOS 0.2.5 and LNP
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Newsgroups:
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lugnet.robotics.rcx.legos
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Date:
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Wed, 17 Jan 2001 22:57:54 GMT
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Viewed:
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1346 times
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> Yesterday I downloaded legOS 0.2.5 and peeked at the code. • Btw. README is
> not up to date.
Ooops... :-) Changed to 0.2.5 version inside.
> For last two month I was working with a friend of mine on a • transport
> protocol implemented on top of LNP for the transmission of • packets of
> unlimited size and with acknowledgements. This was meant • mainly as way for
> a PC to communicate with an RCX without bothering with • collisions, lost
> packets, retransmissions... (I know that there is a program • which works as
> gateway between TCP and LNP, but on the RCX you still have to • write code to
> communicate and (but I'm not sure) it have no acknowledgments. • To cut time
> in programming and, above all, in debugging, I decided to write • code that
> could be run both on Linux and on legOS, using preprocessor • directives
> where necessary. I wanted to use the same lnp.c on both • platforms and so I
> studied LNP in depth (but not so deep to reach the interrupt • calling
> mechanism).
Interesting. I'm always working (but I'm in a "no time period")
in a port for LNPD on Win32 and everything that could clean up
code for LNP is welcome!
> This is the introduction, now comes the real stuff. In version • 0.2.3
> lnp_addressing_write() and lnp_integrity_write() were not • thread-safe. The
> patch applied in 0.2.4 fixes this, but it raises two problems:
>
> 1. Now lnp_logical_write() is no more thread-safe. Furthermore • calling
> lnp_logical_write() screw up the semaphore (tx_sem) and so • the other two
> lnp_XXX_write() become thread-unsafe.
>
> 2. On the host computer LNP is still thread unsafe.
>
> I fix this in my work. I wonder if there is some interest in a • patch to
> apply to the ufficial distribution.
We are surely interested in it. You can upload the patch on
legos.sourceforge.net in the patch section or send it to one of
the developers. If you like, I can apply it for you on official
distribution.
> During my perusuals I noticed two points that can be improved • in lnp.c.
> The function lnp_checksum() computes a 16-bit checksum, while • LNP uses only
> the 8 low order bits. Removing some lines of unuseful code can • speed up
> the function. The other interesting thing is how • lnp_integrity_byte()
> checks the incoming message for integrity. When all data is • received it
> computes the checksum and compare it with the checksum read • from the IR
> port. Then it calls the handler set up by the user program, • and that
> handler probably copies the received packet in a buffer for • later
> inspection. So the packet is read two times during the same • interrupt
> call, while previous calls of the same interrupt did very • little work. It
> seems to me a good idea to generate the checksum as data • arrives, easing
> the burden of the last call. An alternative could be to • compute the
> checksum immediatly after receiving the last data byte, but • before the
> arrival of the checksum byte.
Both things are interesting and if you can post the patch they
will be included in legOS distribution. :-)
Let me know!
Bye,
Paolo.
---
A good imagination unfortunately also makes for vivid nightmares.
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 | | LegOS 0.2.5 and LNP
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| Yesterday I downloaded legOS 0.2.5 and peeked at the code. Btw. README is not up to date. For last two month I was working with a friend of mine on a transport protocol implemented on top of LNP for the transmission of packets of unlimited size and (...) (24 years ago, 17-Jan-01, to lugnet.robotics.rcx.legos)
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