162
ATmega8515(L)
2512A–AVR–04/02
Boot Loader Support
– Read-While-Write
Self-Programming
The Boot LoaderSupport provides a real Read-While-Write Self-Programming mecha-
nism fordownloading and uploading program code by the MCU itself.Thisfeature
allows flexibleapplication softwareupdatescontrolledbythe MCU using a Flash-resi-
dent Boot Loaderprogram. The Boot Loaderprogram can useany available data
interfaceand associatedprotocol to readcodeandwrite (program) that codeintothe
Flash memory, orread the code from the program memory.The program code within
the Boot Loadersection has the capability to write into theentire Flash, including the
Boot Loader memory.The Boot Loadercan thus even modify itself, and it can also
eraseitself from the codeif the featureis not needed anymore. The sizeof the Boot
Loader memory isconfigurable withfuses and the Boot Loaderhas two separate sets of
Boot Lock bitswhich can be set independently.This gives theuser a unique flexibility to
select different levels ofprotection.
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 ofseveralbytes(see Table89 on page
179
) usedduring programming. The page organization does not affectnormal
operation.
Application and Boot
Loader Flash Sections
The Flash memory is organized in twomainsections, theApplication section and the
Boot Loadersection (see Figure 72).The sizeof the different sections isconfiguredby
the BOOTSZ Fuses asshowninTable 78onpage 173 andFigure 72. Thesetwo sec-
tionscan have different level ofprotection sincetheyhave different sets ofLock bits.
Application Section TheApplication section is the section of the Flash that is usedforstoring theapplication
code. The protection levelfor theApplication section can be selectedbytheapplication
Boot Lock bits(Boot Lock bits 0), see Table 74onpage 165. TheApplication section
can neverstoreanyBoot Loadercode sincethe SPM instruction isdisabledwhen exe-
cutedfrom theApplication section.
BLS – Boot Loader Section WhiletheApplication section is usedforstoring theapplication code, the Boot Loader
softwaremust be located in the BLS sincethe SPM instruction can initiate a program-
ming when executing from the BLS only.The SPM instruction can access the entire
Flash, including the BLS itself.The protection levelfor the Boot Loadersection can be
selectedbythe Boot LoaderLock bits(Boot Lock bits 1), see Table 75onpage 165.
Read-While-Write and No
Read-While-Write Flash
Sections
Whether the CPUsupports Read-While-Write or if the CPU ishaltedduring a Boot
Loadersoftwareupdate isdependent on which address that isbeing programmed. In
addition to thetwo sections that are configurable by the BOOTSZ Fuses asdescribed
above, the Flash is also divided into two fixedsections, theRead-While-Write (RWW)
section and the NoRead-While-Write (NRWW) section. The limit between theRWW-
andNRWW sections is giveninTable 79 on page 173 andFigure 72onpage 164. The
main difference between thetwo sections is:
• When erasing orwriting a page located insidetheRWW section, the NRWW section
can be readduring theoperation.
• When erasing orwriting a page located insidethe NRWW section, the CPU ishalted
during the entireoperation.
(24 Seiten)
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