braiden.org

I’ve taken a break from my Verilog programming to better understand USB. My goal is to create some sort of FPGA data processor running over high-speed USB. The BASYS board includes a Cypress EZ-USB FX2 controller. I think the BASYS also comes with software for communicating with the board, but its windows only and a closed api so I haven’t looked into this at all. I’m trying to replace the Digilent’s firmware for the EZ-USB. This post covers some of what I’ve done so far.

I’m burried under lots of documentation. I’ve only read about 25%.

• – The Cypress EZ-USB FX2 Technical Reference
• – The Intel 8051 uC
• – The USB 2.0 Specification
• – The Small Device C Compiler (sdcc)

The Cypress EZ-USB FX2

This devices has a couple of clever features. First, it includes a microcontroller (an Intel 8051 clone) which handles all the USB houskeeping. The microcontroller can handle the usb configuration, enumeration, and control packets. The CPU isn’t required for the bulk of data transfer. The FPGA directly interfaces with a memory buffer removing any possible bottlenecks.

Second, the device supports a software firmware loader. This is great since it means i can replace the propritary code which normally runs on the chip. Once a new firmware has been loaded, it can cause the device to simulate a disconnect/connect forcing the host to  re-enumerate the device capabilities.

Linux Development

This page has a quick overview of using the EZ-USB in linux.

• – fxload, from linux hotplug, is a frimware loader supporting the EZ-USB
• – sdcc, is a c compiler supporting the 8051 uC inside the EZ-USB

Both softwares are apt-get’able on ubuntu.

Theres a simple sample project in SVN.

My Development Progress

I’ve created a very simple firmware;

#include "fx2regs.h"

int main() {

  USBCS |= bmDISCON;
  USBCS &= ~(bmRENUM);
  USBCS &= ~(bmDISCON);

  return 0;
}

This is a very short program. It sets the DISCON bit (causing the EZ-UZB to disconnect from the USB bus), then sets the RENUM bit (causing the EZ-USB, instead of firmware, to take over all usb control functions). When it resets DISCON the EZ-USB connects to the PC and enumerates using its default settings.

The default USB descriptors for the EZ-USB are well documents in its technical reference. I hope to reuse one of its default configurations and let the EZ-USB do most of USB management.

I wrote a little libusb program in C to test things out (SVN). Each USB device has a configuration hierarchy. Configuration -> Interface(s) -> AltSettings -> Endpoint(s). The test program sets the configuration, interface, and altsettings. Looking in /sys/bus/usb, I was able to confirm the expected endpoints were showing.

I’m hoping I can use one these endpoints without anymore coding, but I have to finish up my reading on accessing the FIFO externally.

Tags: 8051, c, usb

This entry was posted on Saturday, September 6th, 2008 at 8:10 pm and is filed under Hardware, Software. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.