atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 350

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

28. Boot Loader Support – Read-While-Write Self-Programming
28.1
28.2
28.2.1
28.2.2
28.3
350
Boot Loader Features
Application and Boot Loader Flash Sections
Read-While-Write and No Read-While-Write Flash Sections
ATmega32U4
Application Section
BLS – Boot Loader Section
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 applica-
tion 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 (program) that code into the Flash memory, or read the code from the program mem-
ory. 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, and it
can also erase itself 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 differ-
ent levels of protection. General information on SPM and ELPM is provided in
Core” on page 8.
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Note:
The Flash memory is organized in two main sections, the Application section and the Boot
Loader section (see
BOOTSZ Fuses as shown in
have different level of protection since they have different sets of Lock bits.
The Application section is the section 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), see
Boot Loader code since the SPM instruction is disabled when executed from the Application
section.
While the Application section is used for storing the application code, the The Boot Loader soft-
ware must be located in the BLS since the SPM instruction can initiate a programming when
executing from the BLS only. 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), see
Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader soft-
ware update is dependent on which address that is being programmed. In addition to the two
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
Code Efficient Algorithm
Efficient Read-Modify-Write Support
1. A page is a section in the Flash consisting of several bytes (see
used during programming. The page organization does not affect normal operation.
(1)
Size
Figure
Table 28-2 on page
Table 28-8 on page 364
28-2). The size of the different sections is configured by the
Table 28-3 on page
354. The Application section can never store any
354.
and
Figure
28-2. These two sections can
Table 29-11 on page
See “AVR CPU
7766A–AVR–03/08
370)