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Рыбницкий Филиал Приднестровского Государственного Университета им.Т.Г.Шевченко

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AVR / datasheets / AT90USB82_162.pdf

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Simple Assembly Code Example for a Boot Loader

228

;-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
subi	ZL, low(PAGESIZEB)	;restore pointer
sbci	ZH, high(PAGESIZEB)	;not required for PAGESIZEB<=256
ldi	spmcrval, (1<<PGWRT) \| (1<<SPMEN)
call	Do_spm
; re-enable the RWW section
ldi	spmcrval, (1<<RWWSRE) \| (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:
elpm	r0, Z+
ld	r1, Y+
cpse	r0, r1
jmp	Error
sbiw	loophi:looplo, 1	;use subi for PAGESIZEB<=256
brne	Rdloop

7707A–AVR–01/07

; return to RWW section

; verify that RWW section is safe to read

Return:
in	temp1, SPMCSR
sbrs	temp1, RWWSB	; If RWWSB is set, the RWW section is not ready yet
ret
; re-enable the RWW section
ldi	spmcrval, (1<<RWWSRE) \| (1<<SPMEN)
call	Do_spm
rjmp	Return

Do_spm:

;check for previous SPM complete Wait_spm:

in temp1, SPMCSR sbrc temp1, SPMEN rjmp Wait_spm

;input: spmcrval determines SPM action

;disable interrupts if enabled, store status in temp2, SREG

cli

;check that no EEPROM write access is present Wait_ee:

sbic EECR, EEPE rjmp Wait_ee

;SPM timed sequence

out SPMCSR, spmcrval spm

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

ret

AT90USB82/162 Boot

In Table 29 through Table 31, the parameters used in the description of the Self-Programming

Loader Parameters

are given.

Table 29. Boot Size Configuration() (16k)

DEVICE

BOOTSZ1

BOOTSZ0

Boot Size (in bytes)

Pages

Application Flash Section

(byte address)

Boot Loader Flash Section (byte address)

End Application Section

Boot Reset Address (Start Boot Loader Section)

512 bytes

0x0000

- 0x3DFF

0x3E00 - 0x3FFF

0x3DFF

0x3E00

16Kb

1024 bytes

0x0000

- 0x3BFF

0x3C00 - 0x3FFF

0x3BFF

0x3C00

2048 bytes

0x0000

- 0x37FF

0x3800 - 0x3FFF

0x37FF

0x3800

4096 bytes

0x0000

- 0x2FFF

0x3000 - 0x3FFF

0x2FFF

0x3000

512 bytes

0x0000

- 0x1DFF

0x1E00 - 0x1FFF

0x1DFF

0x1E00

8Kb

1024 bytes

0x0000

- 0x1BFF

0x1C00 - 0x1FFF

0x1BFF

0x1C00

2048 bytes

0x0000

- 0x17FF

0x1800 - 0x1FFF

0x17FF

0x1800

4096 bytes

0x0000

- 0x0FFF

0x1000 - 0x1FFF

0x0FFF

0x1000

229

7707A–AVR–01/07

(Page size = 64 words = 128 bytes)

The different BOOTSZ Fuse configurations are shown in Figure 92.

Table 30. Read-While-Write Limit(1)

Device	Section	Pages	Address

16K	Read-While-Write section (RWW)	96	0x0000 - 0x2FFF

	No Read-While-Write section (NRWW)	32	0x3000 - 0x3FFF

8K	Read-While-Write section (RWW)	32	0x0000 - 0x0FFF

	No Read-While-Write section (NRWW)	32	0x1000 - 0x1FFF

Note: 1. For details about these two section, see “NRWW – No Read-While-Write Section” on page 218 and “RWW – Read-While-Write Section” on page 218.

Table 31.

Explanation of different variables used in Figure 94 and the mapping to the Z-pointer

			Corresponding	Description(1)
Variable			Z-value	Description(1)
PCMSB		12		Most significant bit in the Program Counter.
				(The Program Counter is 13 bits PC[12:0])

PAGEMSB		5		Most significant bit which is used to address
				the words within one page (64 words in a
				page requires six bits PC [5:0]).

ZPCMSB			Z13	Bit in Z-pointer that is mapped to PCMSB.
				Because Z0 is not used, the ZPCMSB
				equals PCMSB + 1.

ZPAGEMSB			Z6	Bit in Z-pointer that is mapped to PCMSB.
				Because Z0 is not used, the ZPAGEMSB
				equals PAGEMSB + 1.

PCPAGE		PC[12:6]	Z13:Z7	Program Counter page address: Page
				select, for Page Erase and Page Write

PCWORD		PC[5:0]	Z6:Z1	Program Counter word address: Word
				select, for filling temporary buffer (must be
				zero during Page Write operation)

Note: 1.	Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.

See “Addressing the Flash During Self-Programming” on page 223 for details about the use of Z-pointer during Self-Programming.

230

7707A–AVR–01/07

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