ATmega328P datasheet(273/448 Pages) ATMEL

273 / 448 page

273

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

25.2.5

Simple Assembly Code Example for a Boot Loader

Note that the RWWSB bit will always be read as zero in ATmega48PA. Nevertheless, it is rec-

ommended to check this bit as shown in the code example, to ensure compatibility with devices

supporting Read-While-Write.

;-the routine writes one page of data from RAM to Flash

; the first data location in RAM is pointed to by the Y pointer

; the first data location in Flash is pointed to by the Z-pointer

;-error handling is not included

;-the routine must be placed inside the Boot space

; (at least the Do_spm sub routine). Only code inside NRWW section can

; be read during Self-Programming (Page Erase and Page Write).

;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),

; loophi (r25), spmcrval (r20)

; storing and restoring of registers is not included in the routine

; register usage can be optimized at the expense of code size

;-It is assumed that either the interrupt table is moved to the Boot

; loader section or that the interrupts are disabled.

.equ PAGESIZEB = PAGESIZE*2

;PAGESIZEB is page size in BYTES, not words

.org SMALLBOOTSTART

Write_page:

; Page Erase

ldi

spmcrval, (1<<PGERS) | (1<<SELFPRGEN)

rcallDo_spm

; re-enable the RWW section

ldi

spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)

rcallDo_spm

; transfer data from RAM to Flash page buffer

ldi

looplo, low(PAGESIZEB)

;init loop variable

ldi

loophi, high(PAGESIZEB)

;not required for PAGESIZEB<=256

Wrloop:

r0, Y+

r1, Y+

ldi

spmcrval, (1<<SELFPRGEN)

rcallDo_spm

adiw ZH:ZL, 2

sbiw loophi:looplo, 2

;use subi for PAGESIZEB<=256

brne Wrloop

; execute Page Write

subi ZL, low(PAGESIZEB)

;restore pointer

sbci ZH, high(PAGESIZEB)

;not required for PAGESIZEB<=256

ldi

spmcrval, (1<<PGWRT) | (1<<SELFPRGEN)

rcallDo_spm

; re-enable the RWW section

ldi

spmcrval, (1<<RWWSRE) | (1<<SELFPRGEN)

rcallDo_spm

; read back and check, optional

ldi

looplo, low(PAGESIZEB)

;init loop variable

ldi

loophi, high(PAGESIZEB)

;not required for PAGESIZEB<=256

subi YL, low(PAGESIZEB)

;restore pointer

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