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authorAJM <poslathian@poslathian.(none)>2010-05-20 22:47:59 -0400
committerAJM <poslathian@poslathian.(none)>2010-05-20 22:47:59 -0400
commitdcc4c457f0cad15b9d60e8fc3afa913bacacdbc6 (patch)
treead805c404ec1414a330aad74fb833137a44ad136 /core/usb/README
parent3d0c8c9b374a9a2e3e9fb296cf8a89239106eea2 (diff)
downloadlibrambutan-dcc4c457f0cad15b9d60e8fc3afa913bacacdbc6.tar.gz
librambutan-dcc4c457f0cad15b9d60e8fc3afa913bacacdbc6.zip
moved the usb directory to its proper home in ./libmaple
also, removed some old usb file, bootVect.h, which setup the static table for the runtime usb lib that no longer exists and was provided by the bootloader rev 1
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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.
-
-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. Additionally, the usb lib here relies on low level hardware functions that were
- just ripped out of the bootloader code (for simplicity) but clearly this should be replaced with
- direct accesses to functions provided elsewhere in libmaple.
-
- 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) \ No newline at end of file