[fpc-pascal] USB Human Interface Devices

[Stefan V. Pantazi]

The obvious first thing to make sure is that the calling convention 
matches the library for the platform. I see that in 
https://github.com/Zaaphod/pas-libusb/blob/Hack/src/libusb.pas 9line 46)
the calling convention on Windows is cdecl (the stdcall is commented 
out). In libusbxhid, if I remember correctly, the calling convention for 
windows dlls is set to stdcall.

One other thing is that debugging is much more tedious without an 
integrated debugger that allows you to step through each line before you 
can see which function call blows up with a segfault.



On 8/17/19 9:00 AM, James Richters wrote:
> I’m trying to figure out why I get an access violation when I try to open my device with pas-libusb but it works with libusbxhid  they both are using libusb-1.0.dll
> 
>   
> 
> I put a bunch of hacks into pas-libusb to try to figure it out… just a lot of writeln’s so I can try to track down exactly what’s happening.  Because if I try to trace through the program I get “Program received signal SIGSEGV  Segmentation fault” before I get to the problem
> 
>   
> 
> I put this in a branch here:
> 
>   
> 
> https://github.com/Zaaphod/pas-libusb/tree/Hack/src
> 
>   
> 
> I’m using testopendevic_vidpid2.pas to test it with.
> 
>   
> 
> Here’s my output:
> 
> start
> 
> 1
> 
> 2
> 
> a05472131
> 
> a10CEEB93
> 
> b
> 
> c
> 
> FALSE  8086  10CE  A36D  EB93
> 
> FALSE  8087  10CE  0AAA  EB93
> 
> FALSE  0424  10CE  2734  EB93
> 
> FALSE  1D50  10CE  6015  EB93
> 
> FALSE  1B1C  10CE  0C15  EB93
> 
> TRUE  10CE  10CE  EB93  EB93
> 
> FALSE  05E3  10CE  0610  EB93
> 
> FALSE  04E8  10CE  61F5  EB93
> 
> FALSE  1B1C  10CE  0C10  EB93
> 
> FALSE  0424  10CE  274C  EB93
> 
> FALSE  047D  10CE  1020  EB93
> 
> FALSE  1B1C  10CE  1B4F  EB93
> 
> FALSE  1A40  10CE  0101  EB93
> 
> FALSE  0C45  10CE  7403  EB93
> 
> FALSE  10C4  10CE  EA60  EB93
> 
> d
> 
> e
> 
> H1
> 
> I
> 
> 4
> 
> Cousldn't connect to device: Access violation
> 
>   
> 
>   
> 
>   
> 
> Here’s as far as I could get….
> 
> (**
> 
> * Find endpoint according to MatchFunc
> 
> *
> 
> * @param MatchFunc  method to compare a given endpoint descriptor with a
> 
> *                   criterion
> 
> *
> 
> * @returns endpoint or Nil
> 
> *)
> 
> Function TLibUsbInterface.FindEndpoint(MatchFunc : TLibUsbEndpointMatchMethod) : Plibusb_endpoint_descriptor;
> 
> Var IEP : Integer;
> 
>      ED  : Plibusb_endpoint_descriptor;
> 
> Begin
> 
>     writeln('H',FInterface^.bNumEndpoints);
> 
>    For IEP := 0 to FInterface^.bNumEndpoints-1 do
> 
>      Begin
> 
>      Writeln('I');
> 
>        ED:= @(FInterface^.endpoint^[IEP]);
> 
>        if MatchFunc(ED) then
> 
>          Begin
> 
>             Writeln('J');
> 
>             Exit(ED);
> 
>          End
> 
>        else
> 
>         Writeln('K');
> 
>      End;
> 
>    Result := Nil;
> 
> End;
> 
> MatchFunc(ED) is where the access violation occurs, but I can’t trace any further because I can’t find the function MatchFunc()   I just don’t understand where the actual function is.
> 
>   
> 
> Maybe I made an error in the way I’m trying to open the device?   It can’t be any problem with the device itself or using libusb-1.0.dll because that is all working with libusbxhid.. in fact I have all inputs from my device mapped out.. Still don’t have the LCD working…. I can just use libusbxhid, but this is bugging me and I wanted to try to figure out what’s going on.
> 
>   
> 
>   
> 
> James
> 
>   
> 
> 
> 
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
> 

-- 
_______________________________________________________