Rainbow-electronics ATmega8515L Uživatelský manuál stáhnout pdf (Strana 163)

163

ATmega8515(L)

2512A–AVR–04/02

Note that theusersoftware can neverread anycodethat islocated insidetheRWW

section during a Boot Loadersoftwareoperation. The syntax “Read-While-Write sec-

tion” refers to which section that isbeing programmed(erased orwritten), not which

section that actually isbeing readduring a Boot Loadersoftwareupdate.

RWW – Read-While-Write

Section

If a Boot Loadersoftwareupdate isprogramming a page insidetheRWW section, it is

possibletoreadcode from the Flash, but only codethat islocated in the NRWW sec-

tion. Duringanon-going programming, the softwaremustensurethat theRWW section

never isbeing read. If theusersoftwareis trying to readcodethat islocated insidethe

RWW section (i.e.,bya call/jmp/lpmor an interrupt)during programming, the software

mightend up in an unknown state. To avoid this, theinterruptsshould eitherbe disabled

or moved to the Boot Loadersection. The Boot Loadersection is always located in the

NRWW section. TheRWW Section Busy bit (RWWSB) in the StoreProgram Memory

Control Register(SPMCR)will be read aslogical one aslong as theRWW section is

blockedforreading. After a programming iscompleted, theRWWSB must be clearedby

software before reading code located in theRWW section. See “StoreProgram Memory

Control Register – SPMCR” on page 166. fordetails on how to clear RWWSB.

NRWW – No Read-While-Write

Section

The code located in the NRWW section can be readwhen the Boot Loadersoftwareis

updating a page in theRWW section. When the Boot Loadercodeupdates the NRWW

section, the CPU ishaltedduring the entire page eraseorpage write operation.

Figure 71. Read-While-Write vs. NoRead-While-Write

Table 73. Read-While-Write Features

Which Section does the Z-

pointer Address during the

Programming?

Which Section Can be

Read during

Programming?

Is the CPU

Halted?

Read-While-

Write

Supported?

RWW section NRWW section No Yes

NRWW section None YesNo

Read-While-Write

(RWW) Section

No Read-While-Write

(NRWW) Section

Z-pointer

Addresses RWW

Section

Z-pointer

Addresses NRWW

Section

CPU is Halted

during the Operation

Code Located in

NRWW Section

Can be Read during

the Operation

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