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authorAJM <poslathian@poslathian.(none)>2010-04-11 14:28:08 -0400
committerbnewbold <bnewbold@robocracy.org>2010-05-20 22:09:15 -0400
commit85fb99616fee3b1973ac760ce3b5143686c9dfc5 (patch)
treec5cdc1656108290f850a50d30767aa6626d0ea26 /libmaple/usb/README
parent9088e1df65a6f7c223e20f2bc83a6da63161d300 (diff)
downloadlibrambutan-85fb99616fee3b1973ac760ce3b5143686c9dfc5.tar.gz
librambutan-85fb99616fee3b1973ac760ce3b5143686c9dfc5.zip
removed usb files from the libmaple into the application level core lib.
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-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 \ No newline at end of file