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Diffstat (limited to 'libmaple/usb/README')
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diff --git a/libmaple/usb/README b/libmaple/usb/README new file mode 100644 index 0000000..035b566 --- /dev/null +++ b/libmaple/usb/README @@ -0,0 +1,37 @@ +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. + + 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
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