[fpc-pascal] USB Human Interface Devices

[James Richters]

Well..  It doesn’t always work just reading constantly and writing in a different thread.. 

So I have my fast read loop always reading then my LCD write loop sending the 3 packets every 0.3 Seconds.. and it functions ok, and I don’t miss too many counts... but every so often I get this message:
libusb: warning [handle_timeout] async cancel failed -5 errno=0

I have a timeout on my read loop of 10ms.  I tried setting that to 0 so it would just wait for input in it's thread.. but when I do that I get this as soon as I attempt to write to it:
An unhandled exception occurred at $00007FFF189F03C6:
EAccessViolation: Access violation
  $00007FFF189F03C6
  $00007FFF189EDA21
  $00007FFF17AAA1A1
  $00007FFF17AA9CB5
  $000000006B607FFB
  $000000006B6081E7
  $000000006B60C695
  $000000006B605D6F
  $000000006B607E40
  $000000010001B1CA
  $00000001000021BF  main,  line 445 of whb04b-4_test.pas
  $00000001000022B6
  $000000010000EC20
  $0000000100001880
  $00007FFF17B47E94
  $00007FFF18A4A251

Also if I put in a really long timeout like 1000ms I get that.  Line 445 is 
libusbhid_set_report(device_context, HID_REPORT_TYPE_FEATURE, $6 , 8 , WhB04_Packet1 );

so I can't write while I'm reading or waiting for a read after all.

So I came up with a scheme to set all the variables in the slow loop then set a Boolean variable when it's done.. then the fast loop checks for the flag if it is idle for a time, meaning it's not trying to keep up with input.. and that does work.. and I don't miss many counts... but it does miss a few... but I STILL get this 
libusb: warning [handle_timeout] async cancel failed -5 errno=0

even though as far as I can tell, I can't possible be reading and writing at the same time.

I've updated my test project here: https://github.com/Zaaphod/libusbxhid/blob/master/WHB04B-4_test.pas 

I don't really know what libusb: warning [handle_timeout] async cancel failed -5 errno=0 is trying to tell me... it is having an issue canceling waiting for data after the time out I guess.. but why is that a problem? 

Any Ideas?

James

-----Original Message-----
From: fpc-pascal <fpc-pascal-bounces at lists.freepascal.org> On Behalf Of James Richters
Sent: Wednesday, August 21, 2019 8:30 AM
To: 'FPC-Pascal users discussions' <fpc-pascal at lists.freepascal.org>
Subject: Re: [fpc-pascal] USB Human Interface Devices

I FINALLY wrote some data to the LCD!!   YAY !!!   I was trying to get the python application to work.. without any luck.. but I ended up going ahead and trying Zadig changing the driver to libusb-win32...  After I gave up on Python, I went back to FPC and just ran my existing sample program, and I noticed where it used have an error sending to device, it now said 8 bytes sent!!  It's very strange I could read it just fine but not write to it without messing with the driver... but it's working now!

I tried suspending the read thread to write to it.. and well it must have ended up suspending in the middle of a read because the whole thing locked up.. so I just tried as suggested and let it keep reading in a tight loop in it's own thread and then just throw in a write every few seconds on the main program.. and that actually worked fine.. I guess libusb takes care of worry about finishing a read before writing.. I think I did see libusb had something to do with threads.

So now it's just a matter of small details.     The display is a little odd... in that instead of sending it just a real number, you send it an integer for the numbers before the decimal and another integer for the numbers after the decimal.. but it's 2 bytes for each (4 bytes total)  but they are in reverse order.. I need to send LowByte_Integer, High_Byte_Integer, LowByte_decimal, High_Byte_decimal  so the bits from a 16 bit integer end up being 76543210,FEDCBA98  I think this is that edian byte order thing that was mentioned.  I'm just curious if there is already a function available to reverse these like this.. or if I just need to write my own.  It's just some rotates and then split it, so I can do that, but I'm just wondering if there is something already there to do this.. I seem to recall that this kind of thing needs to happen quite a bit.

Also I need to stick a $06 in front of all my packets to send to the device.  I have my data all in arrays,  so I want to do something like this Device_Array[0]:=$06; Device_Array[1..7] := LCD_Array[0..6] ; 

Ah.. but that doesn't work.. is there a way to do this with syntax or do I just need to make a loop to copy the array elements the way they need to be?

James
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