The rhythm game adapter work has basically been stalled for the last two weeks waiting on the microprocessor vendor, FTDI, to try and come up with any type of resolution for the problems I’ve found in their firmware. While they have been gracious to respond at all, until now the responses have been less than useful. If I had an alternate platform with the same properties that had open firmware, or at least a source license, I would switch to it in a heartbeat at this point.
First things first, I am using the VNC2 from FTDI for this project largely because it is the only part I have found that has both a USB slave and an independent USB host controller on the same chip. Plenty of microcontrollers have a USB OTG controller, but that only lets you use one modality at a time. For the USB HID proxying to work, you need to have both simultaneously. One alternative would be to use a micro with a built in USB controller, then an external serial interface controller to handle the other end. Or you could just use two USB enabled microcontrollers, like an AVR, back to back. My goal on this project was to keep the part cost below $10, so that it could be produced in large quantities. Unfortunately AVRs with enough memory to hold a reasonable USB host stack are much more expensive even in quantity than the VNC2, much less the fact that you would need two of them. As far as external USB controllers, you can’t seem to find any low/full speed external controllers that are any cheaper than an entire microcontroller
In the hope that someone has had similar problems and knows how to work around them, I am going to start cataloging all the problems I’ve had with the FTDI toolchain and firmware here on my website. If nothing else, that will give me a clear record of what they may have fixed in subsequent versions.
One thing I am considering, although hesitantly, is reverse engineering enough of the register level interface to the peripherals on the chip to fix the problems myself. As part of debugging some of these other issues, I’ve been hand assembling bits of code to patch interrupt vectors and their code. However, looking through binutils, it isn’t hard to guess that bringing up a brand new architecture with 0 documentation is likely to take several man months of effort, which is a rather large yak to shave for such a small project.