It appears an interface DLL is what you need - this might be what you're
looking for:
https://www.silabs.com/products/mcu/Pages/USBXpress.aspx

Mike=20

-----Original Message-----
From: sftalk-bounce_at_forth.com [mailto:sftalk-bounce_at_forth.com] On Behalf
Of Alan Furman
Sent: Wednesday, October 21, 2009 3:28 PM
To: sftalk_at_forth.com
Subject: [sftalk] USB from SwiftForth

I need help in talking to a USB peripheral from SwiftForth. I have not
found an adequate amount of information anywhere.

Briefly, I am designing a circuit on a small board that generates a few
simple pulses, under the control of a PC app that sends three bytes to
it over the USB. The circuit is one chip, the Silicon Labs C8051F320,
which has exactly what I want: price, functionality, complete USB
hardware on-chip, SwiftX support.

Software required: host PC app that puts up a GUI dialog and talks to
the target board USB; target app that acts as a USB device and generates
a few very simple pulses. The main apps on both the PC and target are
easy and I have used SwiftForth and SwiftX for years. But dealing with
USB is a very big problem.

The actual USB communication required is trivial: transmit three bytes.
I found out after much investigation that, bottom line, the least
complex USB modality for such a purpose is the "human interface device"
class in which "reports" of "vendor-defined" bytes are transmitted.

When the SwiftX software and C8051F320DK board were purchased, Forth
Inc. sent me source for a working application: a SCSI flash drive
controller. I will have to adapt the USB port handlers to the HID
class, which in principle I think I can do.

In the PC host app (having passed on generic driver-writing components
like WinUSB) I will have to call the existing HID class drivers which
are nowadays included with Windows. I would need to get a handle to the
peripheral device, to define and send reports, and do other necessary
things. =20

Not only can I find no examples in Forth of USB access, I can not even
find examples in C! I am good at following Petzold's C-based tutorials
and making the appropriate API calls from SwiftForth. But all the
examples in Axelson's USB Complete are in Visual Basic and C#, and the
same goes for the Maxim and Silicon Labs. How do I translate from C# to
SwiftForth? I have searched Google for hours and found no C examples
there either.

Once I have all the descriptors and API calls worked out for sending a
few bytes of generic ("vendor defined") data to a device, and an
implementation in SwiftForth, USB will no longer be a Berlin Wall
obstacle to Forth programmers. But is this feasible?

Alan Furman

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Received on Wed Oct 21 2009 - 16:46:11 PDT