Rainbow Electronics ATmega162V - Manual (Page 226)

226
ATmega162/V
2513E–AVR–09/03
3. Keep the AVR core in Power-down sleep mode during periods of low V
CC
. This
will prevent the CPU from attempting to decode and execute instructions, effec-
tively protecting the SPMCR Register and thus the Flash from unintentional
writes.
Programming Time for Flash
When Using SPM The calibrated RC Oscillator is used to time Flash accesses. Table 93 shows the typical
programming time for Flash accesses from the CPU.
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<
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<
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<
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<
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<
call Do_spm
; read back and check, optional
Table 93. SPM Programming Time
Symbol Min Programming Time Max Programming Time
Flash Write (Page Erase, Page Write,
and Write Lock bits by SPM)
3.7ms 4.5ms