diff options
Diffstat (limited to 'source/bootloader.rst')
| -rw-r--r-- | source/bootloader.rst | 56 |
1 files changed, 28 insertions, 28 deletions
diff --git a/source/bootloader.rst b/source/bootloader.rst index 57833ed..cfbf545 100644 --- a/source/bootloader.rst +++ b/source/bootloader.rst @@ -66,7 +66,7 @@ have embedded USB support. Thus, Maple doesn’t need the extra FTDI chip. Firmware is uploaded via the standard DFU protocol (also used by iPhone and openMoko). Since DFU is a standard, there is no need for custom software running on the host to upload the firmware. Any DFU -compliant program will work. The maple ide is based around +compliant program will work. The Maple IDE is based around :command:`dfu-util`, openMoko’s DFU utility. Using DFU came at a cost, however. The USB port must additionally implement a separate serial port at the same time (we use the CDC ACM class for serial @@ -87,11 +87,11 @@ important what this means, except for two things. 1. Four drivers were necessary to make everything work. 2. IAD is not supported by OS X. -Mac, on the other hand, only supported Compound USB, a different trick -that is not supported by Windows. While a perpetual background +Mac OS X, on the other hand, only supported Compound USB, a different +trick that is not supported by Windows. While a perpetual background bootloader was attractive, it became clear, after much toiling, we -were going to have to write some custom drivers across several -platforms to make everything work this way. +were going to have to write custom drivers across several platforms to +make everything work this way. .. _bootloader-rev3: @@ -103,22 +103,21 @@ Arduino. In Rev 3, the device resets into bootloader mode, which stays alive for a few moments to receive commands, and then jumps to user code. The bootloader is implemented as a DFU device -- just a DFU device, no serial port. This requires one driver for Windows -(:file:`drivers/mapleDrv/dfu` in the Windows IDE directory). As part -of the :ref:`libmaple <libmaple>` library, user code is automatically -supplied with serial support via some behind the scenes work that -happens automatically when you compile (``setupUSB()`` is appended to -``setup()``). This user mode code only implements a CDC ACM class USB -device, giving you functions like ``Usb.print()``. Separating these -two modes fixed the driver issue, required no complicated compound USB -device nonsense, and works well across platforms, requiring only two -drivers (serial and DFU) on Windows. +(:file:`drivers/mapleDrv/dfu` in the Windows IDE directory). + +As part of the :ref:`libmaple <libmaple>` library, user code is +automatically supplied with serial support via some behind the scenes +work (``setupUSB()`` is called from ``init()``). This user mode code +only implements a CDC ACM class USB device, giving you functions like +:ref:`SerialUSB.read() <lang-serialusb-read>`. Separating these two +modes fixed the driver issues and works well across platforms, +requiring only two drivers (serial and DFU) on Windows. However, it is no longer possible to upload code at will, since there -is no bootloader quietly listening in the background. Instead you have -to reset the board, then initiate a DFU transaction. This reset is -performed automatically by the IDE by sending a command over the USB -serial port. You can generate this reset on your own using a Python -script or some other scheme. All you need do is: +is no bootloader quietly listening in the background. Instead, you +must reset the board, then initiate a DFU transaction. The IDE +performs this reset automatically by performing a special sequence of +changes on the USB serial port: 1. Pulse DTR (high and then low, so that you've created a negative edge) @@ -128,15 +127,16 @@ script or some other scheme. All you need do is: negative edge, rather than just ensuring DTR is low. After the reset, the host OS takes a few moments (.5-2 seconds) to -re-enumerate the device as DFU. This delay is unpredictable, and its -the reason the bootloader on Maple Rev3 stays alive for so -long. Sometimes the bootloader was exiting before the OS had even -enumerated the device! Once in bootloader mode, however, -:command:`dfu-util` uploads your sketch into either flash or RAM (DFU -alternate setting 0 or 1, respectively) and resets the board again. -This time, however, no DFU transaction is initiated, and the -bootloader gives way to user code, closing down the DFU pipe and -bringing up the USB serial. +re-enumerate the device as DFU. This delay is unpredictable, and is +the reason the bootloader on Maple Rev 3/Rev 5 stays alive for so +long. (Sometimes, the bootloader was exiting before the OS had even +enumerated the device.) + +Once in bootloader mode, :command:`dfu-util` uploads your sketch into +either flash or RAM (DFU alternate setting 0 or 1, respectively) and +resets the board again. This time, however, no DFU transaction is +initiated, and the bootloader gives way to user code, closing down the +DFU pipe and bringing up the USB serial port. .. .. _bootloader-rev6: |