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52 lines
5.6 KiB
Markdown
52 lines
5.6 KiB
Markdown
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# Usb device hooking and emulation
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This document gives you an overview of how pumptools handles hooking of usb devices. To be more specific, it does that
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by hooking the API calls of the libusb 0.1 library. Why 0.1 and not 1.0? Because that's the version all pump games have
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used so far. However, pumptools is using the libusb 1.0 API for any communication with real usb devices because 0.1 is
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considered deprecated for quite a while now.
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## Architecture: PIUIO example
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The following ASCII diagram depicts the various modules and how they are involved in the flow for handling the USB PIUIO.
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```text
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+--------------+ +--------------+
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| usb-init-fix | | usb-hook-mon |
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| module | | module |
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One update cycle: +--------------+ +--------------+
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4x ctrl out ^ ^
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4x ctrl in | | +----------+
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interleaved +-----------+ +---------+ | | +------------+ | ptapi |
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+----------+ per sensor | | forward | | | | forward | | +--->| piuio |
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| Game PIU +-------------------->| +------------>| +----------+----------------+---------------------------------->| | | | keyboard |
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+----------+ | | | | | | | | | +----------+
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| | | +----------+ | | | +----------+ +--------+ +---------------+ |
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One update cycle: | libusb0.1 | | usbhook | | 4x ctrl out | piuio-exit | | usb-emu | | piuio | | api pumptools +--+
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1x ctrl out | API | | module +---------------------------+ 4x ctrl in | module +---->| module +----->| module +----->| piuio +--+
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(in data on call | | | | +-------------+ interleaved | | +----------+ +--------+ +---------------+ |
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+----------+ return in buffer) | | forward | | forward | piuio-khack | per sensor | | | +-------+
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| Game PRO +-------------------->| +------------>| +----------------------------> | module +----------------->| | | | ptapi | +-----------+
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+----------+ | | | | +-------------+ | | +---->| piuio +--->| libusb1.0 |
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+-----------+ +---------+ +------------+ | real | +-----------+
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+-------+
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```
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Rough idea of how this works:
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* Classic PIU games issue 8 calls via the libusb 0.1 API
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* PRO instead issues only a single call to reduce overhead
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* On a stock PRO OS and setup, this is intercepted by a kernel module
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* All calls that go to libusb0.1 are intercepted by pumptools's `usbhook` module
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* A separate `usb-init-fix` module takes care of some quirks when calling init more than once
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* `usb-hook-mon` is used for logging all intercepted calls for tracing and debugging purpose
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* In general, any calls are forwaded by an internal API exposed by `usbhook` to any hooks registering for them
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* `piuio-khack` intercepts the single ctrl out call issued on PRO by the PIUIO device. It converts it to the call pattern
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equivalent to the classic PIU games. This allows us to transparently handle them further downstream
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* Next comes the `piuio-exit` module which checks whether the the service and test buttons are pressed on a ctrl-transfer
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level (allowing this to be used without any emulation layer by real devices) to exit the process
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* The `usb-emu` module creates an abstraction layer for the libusb 0.1 API calls. Furthermore, it allows for injecting
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fake stub devices if the application requires IO hardware to be available to work
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* The `piuio` module dispatches the in and out ctrl calls, extracts the piuio data from the buffers and hooks it up
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to pumptools's piuio API layer
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* For the API layer, we can have different implementations, e.g. keyboard or a PIUIO driver talking to a real IO using
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libusb 1.0
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