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Diffstat (limited to 'source/bootloader.rst')
| -rw-r--r-- | source/bootloader.rst | 58 |
1 files changed, 29 insertions, 29 deletions
diff --git a/source/bootloader.rst b/source/bootloader.rst index 17cd34b..9280c68 100644 --- a/source/bootloader.rst +++ b/source/bootloader.rst @@ -23,22 +23,22 @@ remake of the core library as well as the upload process. Some of these changes are aesthetic, refactoring and reorganization. Some are performance minded. The changes to the bootloader, however, were implemented to solve some really gritty cross platform issues. Before -delving in to how the Rev1 bootloader worked and how the Rev 3 +delving in to how the Rev 1 bootloader worked and how the Rev 3 bootloader works now, lets look at the features common to both of them and touch a bit on the Arduino setup. This is a fairly involved explanation, with a lot of details that are likely only interesting to a few. If you just want to get the rough idea, skim this article. If you want to start hacking on the bootloader, get in touch with us to get even more info on how this all works. Of course, you can always -checkout the code at github! +`check out the code at github <http://github.com/leaflabs/libmaple>`_! Arduino -^^^^^^^ +------- Arduino is based off of AVR series micro controllers, most of which lack USB support. Thus, boards like the Duemilanove add USB capability via an FTDI USB to Serial converter chip. This chip interfaces with -the AVR over…serial. When you plug an Arduino into a computer only an +the AVR over…serial. When you plug an Arduino into a computer, only an FTDI driver is needed. Since the FTDI chip is separate from the AVR, you can reset the Arduino without closing this USB connection with the FTDI chip. To program an Arduino, the host machine sends a command @@ -50,8 +50,8 @@ and off you go. The whole process is quick, the bootloader doesn’t live for very long, and will exit almost immediately if no upload commands are received. -Maple Rev1: The Horror... -^^^^^^^^^^^^^^^^^^^^^^^^^^^ +Maple Rev 1: The Horror... +--------------------------- Maple is based off the STM32 (ARM cortex M3) series chips, which do have embedded USB support. Thus, Maple doesn’t need the extra FTDI @@ -71,7 +71,7 @@ serial port transactions. There was no reset necessary for uploads. No waiting. The bootloader was always running the background, ready to receive commands. -The problem was that ONLY Linux did this. Windows refused to attach +The problem was that *only* Linux did this. Windows refused to attach more than one driver to a single USB device without repackaging the DFU and CDC ACM into a single IAD Compound Device. It's not terribly important what this means, except for two things. @@ -86,35 +86,35 @@ were going to have to write some custom drivers across several platforms to make everything work this way. Maple Rev3 -^^^^^^^^^^ +---------- Maple Rev 3 takes a completely different tack, more along the lines of 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`). As part of the :ref:`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, there are no complicated compound usb device nonsense, and the -scheme works well across platforms, requiring only two drivers (serial -and DFU) on Windows. +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. 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 +serial port. You can generate this reset on your own using a Python script or some other scheme. All you need do is: -1. Pulse DTR (high and then low, so that youve created a negative +1. Pulse DTR (high and then low, so that you've created a negative edge) -2. Write “1EAF” in ASCII over the serial pipe. This will cause Maple +2. Write "1EAF" in ASCII over the serial pipe. This will cause Maple to reset. Only the first 4 bytes after a negative edge of DTR are - checked for this command, so its important you actually create a + checked for this command, so it's important you actually create a negative edge, rather than just ensuring DTR is low. After the reset, the host OS takes a few moments (.5-2 seconds) to @@ -122,8 +122,8 @@ 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. +: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. |