![](http://datasheet.mmic.net.cn/90000/M44C090-XXX-FL16_datasheet_2360652/M44C090-XXX-FL16_250.png)
250
Atmel ATmega16/32/64/M1/C1 [DATASHEET]
7647K–AVR–12/13
24.7.13 Simple Assembly Code Example for a Boot Loader
;-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<<SPMEN)
call
Do_spm
;
re-enable the RWW section
ldi
spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call
Do_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:
ld
r0, Y+
ld
r1, Y+
ldi
spmcrval, (1<<SPMEN)
call
Do_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<<SPMEN)
call
Do_spm
;
re-enable the RWW section
ldi
spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call
Do_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
sbci
YH, high(PAGESIZEB)
Rdloop:
lpm
r0, Z+
ld
r1, Y+
cpse
r0, r1
jmp
Error
sbiw
loophi:looplo, 1
;use subi for PAGESIZEB<=256
brne
Rdloop