Question: How to pass a streaming channel to C function?

[landon]

I'm trying to pass a streaming channel to a C function so it can stuff the channel with some formatted string data, floats, etc.

I see there is a typedef for chanend which is just an unsigned, but I don't see anything related to the streaming modifier.

In XC, it makes a distinction in the argument list for streaming channels. But there is no "streaming" modifier in the xccompat.h.

How does one pass a streaming channel to a C function? Is there anything special about the streaming channel type vs pure channel (besides their non-sychronous behavior)?

Can channels and streaming channels be interchanged as far as a C function is concerned?

Landon

[skoe]

Just use unsigned like for normal channel ends. The streaming modifier only tells the XC compiler how <: and :> have to be implemented.

However, take care that ordinary channels and streaming channels have to be handled differently in your C code. There's no token handshake for streaming channels.

[landon]

Hi Skoe,

Thanks for the response. I've tried several things to no avail - seems like it would be a trivial thing to solve but I haven't found a way to coerce it.

In the C function, I changed the prototype and fingerprint of the parameter chanend to unsigned, but still error'd out on type conversion.

Leaving the C function parameter as unsigned, I tried casting the streaming chanend variable to (unsigned) in the call from XC to C. Still got type conversion errors.

I still can't find the right combination.

Here's what I have tried

XC fragment:

Code: Select all

#include "mycstuff.h"

void executive(streaming chanend txChan )
{
   // ... do some stuff, then call a C function with the channel
   send_command_prompt( (unsigned)txChan );
}

C Fragments:
mycstuff.h

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extern void send_command_prompt( unsigned txChan );

mycstuff.c

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#include "mycstuff.h"

void send_command_prompt( unsigned txChan )
{

}

Fails:

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error: conversion to transmissive type requested

(I've tried "chanend txChan" for the prototype as well passing the streaming chanend which is what originally failed).

If I try type casting the streaming chanend to (unsigned) in XC (adjusting the prototypes in the C to match unsigned), I get:

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 `send_command_prompt' changes streaming qualifier of type

If I leave the C function prototypes as chanend and typecast the streaming channel to (unsigned), I still get the:

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error: conversion from transmissive type requested

I just can't find a combination that will allow me to pass a streaming channel variable as a parameter to a C function.

What am I missing?

Landon

[Folknology]

Don't forget the :

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#include <xccompat.h>

Also lookie using channels and ports in C/C++

regards
Al

[landon]

Thanks, Al, I have looked at the wiki, but it only covers regular channels not streaming channels.

If I remove the streaming modifier, I have no problems with my compiles - the wiki page on channel passing to C works fine.

What I'm lacking is the technique to pass streaming channels to C. Once I try passing a streaming channel, since there is no streaming chanend in C xccompat.h and I can't figure out how to cast it to a regular chanend, I'm getting hung up.

Any hints? Have you tried passing a streaming channel to a C function - there must be some incantation I'm missing to do it.

Thanks for any help,

Landon

[Folknology]

Have a peek into the ethernet mii_wrappers for some clues, their in the ethernet software download , inside should be a use of streaming channels with both XC and C if I recall.

*PS the Ethernet and TCP/IP examples are not the best XS1 examples in the world by the way, but it might give you some clues. Also they use a "streaming" def to document that the chanend is a streaming rather than a regular chanend which is quite a clever idea IMHO.

regards
Al

[landon]

Hi Al,

Thanks for the pointer, I'll definitely take a look at it.

Landon

[landon]

Ha! in mii_wrappers.c

here is the incantation :-)

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#include <xccompat.h>
#define streaming

Then in their function using a streaming channel:

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void mii_rx_pins_wr(port p1,
                    port p2,
                    int i,
                    streaming chanend c)

Wow, didn't realize I could get away with that...ridiculously easy. Clearly I was making it too hard,

Thanks for the pointer to this example - very helpful,

Landon

[landon]

I'm happy to report that I've now got a console user interface implemented on my XK-1 board that uses streaming channels.

I implemented the command line console interface using Ragel (http://www.complang.org/ragel/ ). I used the C implementation of Ragel parser output, integrated it with the rx/tx streaming channel and uart code on XMOS.

The Ragel code built without a hitch in the XDev tools (not too surprising since I've used Ragel in AVR tools before - it's very portable.) Works like a charm,

Landon

[lilltroll]

Maybe someone of you native english speaking could leave a note on that on wiki, chan & streaming chan usages (in C) :!: :?: Please