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diff --git a/core/usb/README b/core/usb/README new file mode 100644 index 0000000..ef4964c --- /dev/null +++ b/core/usb/README @@ -0,0 +1,66 @@ +The USB submodule of libmaple is responsible for: + initilizing the usb peripheral, scaling the peripheral clocks appropriately, + enabling the interrupt channels to usb, defining the usb isr, resetting the usb + disc pin (used to tell the host were alive). Additionally, the usb submodule defines + the virtual com port usb applications that is available to all user sketches via Usb.print() + and others. + +To use it: + Call Usb.init() to enable the IRQ channel, configure the clocks, + pull down usb_disc, and setup the vcom buffers + Usb.print/ln, available(), read(), write() implement the same + interface as Serial1/2/3 + + +Current Status: + Currently, the USB submodule relies on the low level core library provided by ST to access the + usb peripheral registers and implement the usb transfer protocol for control endpoint transfers. + The high level virtual com port application is unfortunately hard to untangle from this low level + dependence, and when a new USB core library is written (to nix ST dependence) changes will likely + have to be made to virtual com application code. Ideally, the new core library should mimick the + form of MyUSB (LUFA), since this library (USB for AVR) is growing in popularity and in example + applications. + + The virtual com port serves two important purposes. 1) is allows serial data transfers between + user sketches an a host computer. 2) is allows the host machine to issue a system reset by + asserting the DTR signal. After reset, Maple will run the DFU bootloader for a few seconds, + during which the user can begin a DFU download operation ('downloads' application binary into + RAM/FLASH). This without this virtual com port, it would be necessary to find an alternative means + to reset the chip in order to enable the bootloader. + + If you would like to develop your own USB application for whatever reason (uses faster isochronous + enpoints for streaming audio, or implements the USB HID or Mass Storage specs for examples) then + ensure that you leave some hook for resetting Maple remotely in order to spin up the DFU bootloader. + Please make sure to give yourself a unique vendor/product ID pair in your application, as some + operating systems will assign a host-side driver based on these tags. + + It would be possible to build a compound usb device, that implements endpoints for both the virtual + COM port as well as some other components (mass sotrage etc.) however this turns out to be a burden + from the host driver side, as windows and *nix handle compound usb devices quite differently. + + Be mindful that running the usb application isnt "free." The device must respond to periodic bus + activity (every few milliseconds) by servicing an ISR. Therefore the usb application should be disabled + inside of timing critical applications. In order to disconnect the device from the host, the USB_DISC + pin can be asserted (on Maple v1,2,3 this is GPIOC,12). Alternatively, the NVIC can be directly configured + to disable the USB LP/HP IRQ's + + This library should exposed through usb.h, do not include any other files direcly in your application. + + The files inside of usb_lib were provided by ST and are subject to their own license, all other files were + written by the LeafLabs team and fall under the MIT license. + +Integration with libmaple: + The current usb lib is ported directly from the maple bootloader code, adapted to be a virtual com rather than + a DFU device. That means several functions are redefined locally that could have been pulled from elsewhere + in libmaple. Thus, ths usb module depends absolutely zero on libmaple, it even ensures that clocks are configured + correctly for its operation. + +Todo: + - write custom low level usb stack to strip out any remaining dependence on ST code + - remove dependence on hardware.c, since any functions here really should have their + own analogues elsewhere inside libmaple + - add a high level usb application library that would allow users to make their own + HID/Mass Storage/Audio/Video devices. + - implement a Usb.link(SerialX) that forces a passthrough + the host computer virtual com to SerialX, and utilizes the + line_config commands correctly (sets baud etc)
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