267
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
1.
If there is no need for a Boot Loader update in the system, program the Boot Loader Lock bits to prevent
any Boot Loader software updates.
2.
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done
by enabling the internal Brown-out Detector (BOD) if the operating voltage matches the detection level. If
not, an external low V
CC reset protection circuit can be used. If a reset occurs while a write operation is in
progress, the write operation will be completed provided that the power supply voltage is sufficient.
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, effectively protecting the SPMCSR Register and thus the
Flash from unintentional writes.
26.7.12
Programming time for flash when using SPM
The calibrated RC oscillator is used to time Flash accesses.
Table 26-6 shows the typical programming time for
Flash accesses from the CPU.
26.7.13
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
Table 26-6.
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