Flash Layout for On-Chip OAD

This section will describe the method for placing images in internal flash when using on-chip OAD.

Constraints and Requirements for On-chip OAD

In order to perform an On-chip OAD the target system must have:

• The user application must be sufficiently small in order to fit into the flash layout system described below

• User app functionality is lost while performing OAD (Persistent app is running)

Only one user application image may be stored in flash at any time.

Internal Flash Memory Layout

The internal flash of the device contains the active user application, the persistent application, and the BIM. Each application’s role is defined below.

Application Name	Description
BIM	Search for the proper image in FLASH Copy new user image Ensure validity and optionally security of image before running
Persistent application	Providing lightweight application that implements the OAD profile
User application	User application Must implement OAD reset service

The user application (referred to as OAD_IMG_B) pictured above is responsible for the following:

• Implementing the OAD reset service

• Implementing customer defined behavior

The persistent application (referred to as OAD_IMG_A) pictured above is responsible for the following:

• Implementing the protocol stack definition of the OAD service

• This image is permanently resident on the device

The location of the persistent application varies depending on the flash size available for the selected device variant. This is done to maximize the user’s application space. Refer to the linker cmd file define IMG_A_FLASH_START to further determine where precisely the persistent application is located.