CODEWITHSUNDEEP
gccassemblyavravr-gcc
THX-1138
THX-1138

Reputation: 21730

GCC (AVR) Assembly: Subtract label address

I am trying to accomplish:

LABEL:
....
subi r18, LABEL

I need to subtract address of a label from a register. How do I do that?

Upvotes: 0

Views: 1017

Answers (2)

THX-1138
THX-1138

Reputation: 21730

subi r16, pm_lo8(LABEL)
sbci r17, pm_hi8(LABEL)

as answered on avrfreaks:
http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=857982#857982

reference document:
http://sourceware.org/binutils/docs-2.21/as/AVR_002dModifiers.html#AVR_002dModifiers

Upvotes: 2

user786653
user786653

Reputation: 30460

Note: I'm not that familiar with AVR assembler, this is just what I could gauge from reading a few webpages. I'm also assuming that your addresses are 16-bit.

; Address you wish to subtract the label from in R16 (low):R17 (high)

SUBI R16, LOW(LABEL)
SBCI R17, HIGH(LABEL) ; Omit this part if you have < 256 Bytes of ram

Upvotes: 1

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