Oad Image Identify (0Xffc1); Figure 6. Oad Service Description - Texas Instruments SimpleLink CC2640 User Manual

0xFFC4 Image Status Status of current OAD download

Figure 6. OAD Service Description

The primary method for sending data from the OAD downloader to the OAD target is the GATT writes
with no response message. GATT notifications are the primary method used to send data from the
target to the downloader. This communication scheme was selected to prevent the target device from
having to include the GATT client code required in order to receive notifications from the downloader.
The downloader shall register for notifications from any characteristic with a CCCD (by writing 01:00 to
the CCCD).
Note that both GATT notifications and GATT write with no response are non-acknowledged message
types. This means that in poor RF conditions, the OAD process may not be successful. There is an
inherent tradeoff between the speed of the OAD process and its reliability. Implementing a reliable
OAD communication protocol (with retries, acknowledgments, etc.) is outside the scope of this
document.
For a message sequence chart describing the OAD process in terms OAD service messages exchanged
between the target and downloader please see .
Figure 11

7.4.1 OAD Image Identify (0xFFC1)

The Image Identify characteristic is used to exchange image metadata between downloader and target.
The OAD process begins when the downloader sends the 16 byte metadata of the proposed OAD image
to the target. Upon receiving the candidate metadata, the target will do some calculations to determine
whether or not the proposed image should be downloaded. "01:00" shall be written to the CCCD of this
characteristic so that notification for metadata rejection is enabled.
Note that the conditions under which an OAD is accepted vary slightly between the on and off chip
methods. Please see the respective sections for more information about image reject conditions.
If the target accepts the image it will continue the OAD process by sending a notification on the Image
Block characteristic requesting the first block. Otherwise the target will reject the image by sending back
a portion the currently resident image's metadata. The reject metadata contains the Image Version,
Image version, and User ID fields. For more information about these fields, please refer to the metadata
section.
A sniffer capture of the image identify characteristic being used to reject a candidate OAD image is
shown below. Note that only image version, length, and user ID are contained in the reject notification.