Datasheet

30.2.4 Programming Time for Flash when Using SPM
The calibrated RC oscillator is used to time Flash accesses. The following table shows the typical
programming time for Flash accesses from the CPU.
Table 30-1. SPM Programming Time
Symbol Min. Programming Time Max Programming Time
Flash write (Page erase, page write, and write
Lock bits by SPM)
3.2ms 3.4ms
Note: Minimum and maximum programming time is per individual operation.
30.2.5 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
.
; must be avoided if the page buffer is pre-filled. Will flush the page
buffer.
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
ATmega48PA/88PA/168PA
Self-Programming the Flash
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 341