Rainbow Electronics ATmega128RFA1 - Manual (Page 450)

450
8266A-MCU Wireless-12/09
ATmega128RFA1
30 Boot Loader Support – Read-While-Write Self-Programming
The Boot Loader Support provides a real Read-While-Write Self-Programming
mechanism for downloading and uploading program code by the MCU itself. This
feature allows flexible application software updates controlled by the MCU using a
Flash-resident Boot Loader program. The Boot Loader program can use any available
data interface and associated protocol to read code and write that (program) code into
the Flash memory, or read the code from the program memory. The program code
within the Boot Loader section has the capability to write into the entire Flash, including
the Boot Loader memory. The Boot Loader can thus even modify itself (including
erasing) from the code if the feature is not needed anymore. The size of the Boot
Loader memory is configurable with fuses and the Boot Loader has two separate sets
of Boot Lock bits which can be set independently. This gives the user a unique flexibility
to select different levels of protection.
30.1 Features
• Read-While-Write Self-Programming
• Flexible Boot Memory Size
• High Security (Separate Boot Lock Bits for a Flexible Protection)
• Separate Fuse to Select Reset Vector
• Optimized Page
(1)
Size
• Code Efficient Algorithm
• Efficient Read-Modify-Write Support
Note: 1. A page is a section in the Flash consisting of several bytes (see "Table 31-7" on
page 467 ) used during programming. The page organization does not affect normal
operation.
30.2 Application and Boot Loader Flash Sections
The Flash memory is organized in two main sections: the Application section and the
Boot Loader section (see
Figure 30-2 on page 452 ). The size of the different sections is
configured by the BOOTSZ Fuses as shown in Table 30-7 on page 461 and Figure 30-2
on page 452 . These two sections can have different level of protection since they have
different sets of Lock bits.
30.2.1 Application Section
The Application section is the region of the Flash that is used for storing the application
code. The protection level for the Application section can be selected by the application
Boot Lock bits (Boot Lock bits 0, BLB0), see
Table 31-2 on page 464 . The Application
section can never store any Boot Loader code since the SPM instruction is disabled
when executed from the Application section.
30.2.2 BLS – Boot Loader Section
While the Application section is used for storing the application code, the Boot Loader
software must be located in the BLS. The SPM instruction can only initiate
programming when executed from the BLS. The SPM instruction can access the entire
Flash, including the BLS itself. The protection level for the Boot Loader section can be
selected by the Boot Loader Lock bits (Boot Lock bits 1, BLB1), see
Table 31-2 on page
464 .