Hi Harry,
I've only skimmed your example code, but off the top of my head here are a
couple things.
The FlightGear serial IO defaults to non-blocking. That means characters
will only be read if they are available, and you can't depend on the entire
message string being there when you try to read it. If you back up to the
routine that actually reads the data in, you may need to do some work there
to accumulate the entire message before handing it off to your parsing
routine.
One thing I do quite often in these situations is to add printf()'s to the
code that reads the data in. Seeing the actual data values or message
lengths that are read each time can be quite instructive.
Best regards,
Curt.
On Mon, Mar 23, 2009 at 3:44 AM, Harry Campigli wrote:
> Could I ask for some help and advise on this issue.
>
> I am trying to interface my Microchip Pic based sim hardware to FG. I have
> it working with a genetic string but the string is becoming to large for the
> pics to handle, also I would like a crc or check sum on the data. Thus i
> prefer a compressed hex format. Ie the pic sends 4 bytes sync,16 bytes each
> bit being a switch boolean, 16 bytes each being an analog setting then 2
> bytes with each bit being a sign on the 16 analogs.
>
> The format thus is A5 5A A5 5A hh hh hh hh hh hh .......for 40 bytes.
>
> For simplicity I opted to clone and adapt the Atlas driver, keeping in line
> with all existing FG conventions. and use it as a frame. and intigrate my
> driver into FG when i build.
>
> So far I have bumbled my way along, I not a good programmer but have learnt
> my way around C with the microchip C18 to drive all the hardware. I have
> managed to generate and output a binary compressed message from FG. But cant
> seem to get it to decode on the inwards stream.
>
>
> My approach is similar to the way i run the can bus between the hardware
> Pics, pick up the char one at a time, check for the first A5, then 3 sync
> chars from "buf" then if ok (synced up), copy the next 40 chars to "msgin".
> If thats ok then it sets a flag to decode the data. for now i also have an
> 0x0D on the end making it 41 chars. Later i intend to add the CRC routine.
> Also I intend to use a network socket to the Pics once its all working. I
> try to work in small steps.
>
> It seems I cant pick up the first A5, as I understand it, "buf" has the
> data in.
>
> My question is how does the low level IO in Sg and FG work, am I wrong to
> work on the premise that every time parse message is called buf contains
> fresh data from the serial, Or does the the low level code require a CR? DO
> i need to set up a static ring buffer os sorts and take the incoming from
> that?
>
>
> Below Is the code as it stands. i would expect to come out of this with
> Msg_CS_OK=1, but maybe its not quite correct, for starters I need to pick up
> the first sync char.
>
>
> I hope i have provided enough info to enable an answer,
> Regards Harry
>
> FYI the OS is suse11.1 but i am not having any problems from that point of
> view.
>
>
>
>
>
> bool FGSim::parse_message() {
> SG_LOG( SG_IO, SG_INFO, "parse atlas message" );
> char msgin[256],dblin[6];
> char a,b,c,d,e,f,g,h,b0,b1,b2,b3,b4,b5,b6,b7,w,starter,Char_Count,ch,l;
> static char Msg_State,Msg_pointer,Message_CS_H,Message_CS_L,Msg_CS_OK;
> double min, max;
> int intin;
> char pbsw;
>
> // string msg = buf;
> // msg = msg.substr( 0, length );
> // SG_LOG( SG_IO, SG_INFO, "entire message = " << msg );
>
> SGPropertyNode * node;
>
>
>
>
> Char_Count = 41; // length
> l =0;
> while(l != Char_Count)
> {
>
> ch = buf[l];
> switch (Msg_State)
> {
> case 0: // find the sync header byte 0
> if(ch == 0xA5)
> {
> Msg_State++;
> Msg_CS_OK = 0;
> b5=false; // test
> to see if value recieved.
> node = fgGetNode("/controls", true);
> node->setBoolValue("gear/gear-down", b5);
> }
>
> break;
>
> case 1: // find the sync header byte 1
> if(ch == 0x5A) {Msg_State++;}
> else Msg_State= 0;
>
> break;
>
> case 2: // find the sync header byte2
> if(ch == 0xA5) {Msg_State++;}
> else Msg_State= 0;
> break;
> case 3: // find the sync header byte 3
> if(ch == 0x5A) {Msg_State++;Msg_pointer=0;} // reset
> counter point for msgin
> else Msg_State= 0;
> break;
>
> case 4:
> msgin[Msg_pointer] =ch;
> Msg_pointer++; // write ch to msgin till all done
> if(Msg_pointer==40){Msg_State++;Msg_CS_OK=1;}
> break;
>
> case 5: // get fist cs byte
> Message_CS_H = ch;
> Msg_State++;
> break;
>
> case 6:
> Message_CS_L =ch;
> Msg_State = 0;
> break;
> default:
> Msg_State=0;
> break;
>
> } // switch
>
>
> l++;
> } // while
>
> .....
>
>
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--
Curtis Olson: http://baron.flightgear.org/~curt/
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Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
easily build your RIAs with Flex Builder, the Eclipse(TM)based development
software that enables intelligent coding and step-through debugging.
Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com
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