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Example:
;This example shows SPM write of one page for devices with page 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)
;- registers used: r0, r1, temp1, temp2, looplo, loophi, spmcrval
; (temp1, temp2, looplo, loophi, spmcrval must be defined by the user)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
.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
;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
;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, 2 ;use subi for PAGESIZEB<=256
brne rdloop
;return
ret
do_spm:
;input: spmcrval determines SPM action
;disable interrupts if enabled, store status
in temp2, SREG
cli
;check for previous SPM complete
wait: in temp1, SPMCR
sbrc temp1, SPMEN
rjmp wait
;SPM timed sequence
out SPMCR, spmcrval
spm
;restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret