What protocol ? its a ram / eprom emulator
c'on man, the USB protocol !!! I neet to attach it to a Linux/MIPS SoC, there is no Windows/x86 inside
does that matter ? the target system is irrelevant. if your MIPS machine has a socket for an Eprom it will work. the OS / CPU doesn't matter.
the emulator has a ram on board with some logic that makes it behave as an eprom. Load the image into the emulator and your MIPS machine is none the wiser. it doesn;t need access to USB. the USB port is for the host machine where you run the development environment.
Oh , wait .. you mean : you want to use this on a MIPS based machine using linux , cause that is your development box ? tough shit sherlock. The prevalent dev hardware is a intel architecture running microsoft stuff. once in a while you may find some linux stuff on intel. But beyond that ? it's a VERY small world.... Things are developed for the market. like it or not , that is still 90% Wintel ...and a bit Lintel and maybe a tiny bit iOS. anything else is esoteric and you will have to resort to homebrew.
Elektor magazine made an eprom emulator in the mid 90's that was using a 62256 ram , some counters and hooked up to a standard printerport.
you would take the binary image of the rom and simply 'copy' it to LPT1.
you had to press a button on the emulator to 'reset it'. you could then simply use a dos command 'copy eprom.bin lpt1:' and that was it.
they later made an rs232 version
https://www.elektormagazine.com/magazine/elektor-200101/16948https://www.elektormagazine.com/magazine/elektor-200101with any luck you can still buy the circuit board. a few dollar for the PDF file and off you go. that may be your best shot.
here's another one (older) :
http://www.davidprojects.net78.net/styled-2/index.htmli built several of the printerport ones. they were mades using SMd and used 74590 and 74593 dual counters that were expensive and hard to find at the time.