Boot Loader
2.3.4 Tiva-Specific USB Download Commands
The DFU class specification provides the framework necessary to download and upload firmware
files to the USB device but does not specify the actual format of the binary data that is transferred.
As a result, different device implementations have used different methods to perform operations
that are not defined in the standard such as:
Setting the address to flash a downloaded binary.
Setting the address and size of the area of flash with contents to be uploaded.
Erasing sections of the flash.
Querying the size of flash and writeable area addresses.
The USB boot loader implementation employs a small set of commands which can be sent to the
DFU device via a DFU_DNLOAD request when the device is in IDLE state. Each command takes
the form of an 8-byte structure that defines the operation to carry out and provides any required
additional parameters.
To ensure that a host application that does not have explicit support for Tiva-specific commands can
still be used to download binary firmware images to the device, the protocol is defined such that only
a single 8-byte header structure must be placed at the start of the binary image being downloaded.
This header and the DFU-defined suffix structure can both be added using the “dfuwrap” command-
line application supplied with TivaWare, thus providing a single binary that can be sent to a device
running the Tiva USB boot loader using a standard sequence of DFU_DNLOAD requests with no
other embedded commands or device-specific operations required. An application which does
understand the Tiva-specific commands may make use of them to offer additional functionality that
would not otherwise be available.
Querying Command Support
Because the device-specific commands defined here are sent to the DFU device in DFU_DNLOAD
requests, the possibility exists that sending them to a device which does not understand the protocol
could result in corruption of that device’s firmware. To guard against this possibility, the USB boot
loader supports an additional USB request which is used to query the device capabilities and allow
a host to determine whether or not the device supports the Tiva commands. A device which does
not support the commands either stalls the request or returns unexpected data.
To determine whether a target DFU device supports the Tiva-specific DFU commands, send the
following IN request to the DFU interface:
bmRequest-
Type
bRequest wValue wIndex wLength Data
10100001b 0x42 0x23 Interface 4 Protocol Info
where the protocol information returned is a 4-byte structure, the first two bytes of which are 0x4D,
0x4C and the second two bytes indicates the protocol version supported, currently 0x01 and 0x00
respectively.
Download Command Definitions
The following commands may be sent to the USB boot loader as the first 8 bytes of the payload to
a DFU_DNLOAD request. The boot loader expects any DFU_DNLOAD request received while in the
16 April 8, 2013
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