On Wednesday, December 09, 2015 11:24:01 PM Peter Stuge wrote: ... > Replacing the FTDI UART with a small USB-capable processor would > allow the best of both worlds - a UART is still the interface to > the STM32F429, but a meaningful USB protocol is the interface to > the host software. > > I had forgotten that the USB interface only needs to be full speed > so I had ruled this option out. > > > There are tons of candidate processors to choose from. I have many > years of experience with the NXP LPC1342/43 Cortex-M3; among other > things I've used it in a workshop on how to create USB devices and > easily write host software. That material is online at http://cbs.stuge.se/ > > The required components given 3.3V are CPU (LQFP48), two ceramic supply > caps, a crystal, two caps for the crystal, two series resistors for USB > D+ and D-, one 1.5k 1% pull-up and one digital transistor or FET to > control USB presence from the device. > > The hardware might even be simpler than for the FT232, the software > allows a good USB host protocol, and with this approach someone will > still have the pleasure of writing a serializer/deserializer, but > with the potential added benefit that they would be running quite > close together and in very similar environments - maybe allowing even > more code reuse.
I agree the hardware stated above is as simple or even simpler than the FT232H we used on the dev-bridge. Pros: * better USB interface from the host side * avoids having FTDI's design choices imposed on us - e.g. gives us ability to set USB VID/PID and other settings without that apparently being re- programmable from the host * more reliable communication between host and alpha * vendor specific interface being the recommended way to go by the one I consider the USB expert in the group Cons: * another MCU for us to program and support * not sure it would be able to match the 40 Mbyte/s [1] claimed for the FT232H? OTOH, I don't think we need that much (now) * some kind of driver (.INF file at least) necessary on Windows (not my main concern) Given the pros and cons I see at this time with the two different proposals, and on the premises that you supply code and schematics (not all of it necessarily, but I'm counting on a well matured boilerplate) and USB/protocol design advice, I've decided to put my vote in favor of your proposal. /Fredrik [1] DS_FT232H.pdf, 4.1 (page 22) "upto 40 Mbytes/second over a synchronous 245 parallel FIFO interface" _______________________________________________ Tech mailing list [email protected] https://lists.cryptech.is/listinfo/tech
