6.112.2 Status Register (SREG) and Boolean Formula

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  ZL, 2
        sbiw  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  looplo, 2                    ; use subi for PAGESIZEB<=256
        brne  rdloop

        ret                                ; return

do_spm:
        in    temp2, SREG                  ; input: spmcrval determines SPM action
        cli                                ; disable interrupts if enabled, store status

wait:
        in    temp1, SPMCR                 ; check for previous SPM complete
        sbrc  temp1, SPMEN
        rjmp  wait

        out   SPMCR, spmcrval              ; SPM timed sequence
        spm

        out   SREG, temp2                  ; restore SREG (to enable interrupts if 
                                           ; originally enabled)
        ret

Words

1 (2 bytes)