OAD Type Comparison

There are two methods of implementing an over the air download update: On-chip and Off-chip. The key difference between the two methods is where the downloaded image is to be stored during the OAD process. During on-chip OAD, the downloaded image is written to internal flash, allowing for a single chip OAD solution. Off-chip stores the downloaded image in an external flash part, requiring a two chip OAD solution. Each type of OAD has associated trade offs and benefits which will be discussed in their respective sections. Despite their differences, both OAD methods share the same over the air profile and image header.

Table 16. OAD Types Overview.

OAD Type	Advantages	Limitations
On-chip	No external flash required	Application size restriction Stack upgrade must erase app (two step upgrade) Stack upgrade must not change stack APIs User app not running during OAD
Off-chip	Ability to store multiple / backup images App + Stack merged update supported Maximum application size availabe to customer	Low power external flash required