Stierlitz, the Fearless, Driver-Less Bus Analyzer.
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Got a Xilinx ML501, or another FPGA board with a Cypress CY7C67300 USB controller on it? Got a bus 31 or fewer bits wide? Stierlitz will sit on your bus and imitate a USB Mass Storage device. The latter will appear to have a FAT16 file system on it, containing a single binary "image" file. Mount it (under Linux, using "mount -o sync ...") and perform arbitrary reads/writes by reading or writing blocks within the image file. Make sure to use the O_DIRECT flag (or "raw" block device, if your kernel still has it) to disable ALL caching on the PC end. AFAIK, you cannot do this on Windows or Mac. Therefore I did not bother testing Stierlitz at all on those poor, crippled systems. If you snip out the FAT16 emulation, you can get 41 bits of address space. You will need: 1) To build the firmware image, you will need an assembler for the Cypress CY16 architecture: "QTASM.EXE". (Get it here: http://www.cypress.com/?rID=14436) 2) EZOTGDBG (https://github.com/asciilifeform/ezotgdbg) to flash the firmware image to the CY7C67300. 3) The Xilinx build tools for your board. Edit the Makefile in the "ml501" directory, esp. if you have a 32-bit Linux. 4) A UCF file to match your board's wiring, if you have something other than an ML501. 5) (Optional) SBCL (http://sbcl.org). See the "Lisp" directory. The "ml501" directory contains a Verilog implementation of the required FPGA-side logic, "stierlitz.v". If you build using the provided Makefile (edit to insert your Xilinx tool paths) you will have a demo. The demo gives you a 128K "file" mapped to SRAM ("infer-sram.v"; need an FPGA with at least this much Block RAM to run this.) Another example, involving an LCD module, can be seen here: http://www.loper-os.org/?p=797