How do I do this AVR assembly more elegantly

Question

I've currently got this code:

// takes a table reference as an argument
.macro load_table_into_r0_to_r8
    ldi ZL, low(2*@0)
    ldi ZH, high(2*@0)
    lpm r25, Z+
    mov r0, r25
    lpm r25, Z+
    mov r1, r25
    lpm r25, Z+
    mov r2, r25
    lpm r25, Z+
    mov r3, r25
    lpm r25, Z+
    mov r4, r25
    lpm r25, Z+
    mov r5, r25
    lpm r25, Z+
    mov r6, r25
    lpm r25, Z+
    mov r7, r25
    lpm r25, Z+
    mov r8, r25
.endm

As you can see, a lot of really similar code is repeated.

It would be ridiculous if there isn't a way to write this in a shorter fashion, like with .irp or maybe .ifs. However, I can't get that to work. For .irp I tried this:

.irp i, 0,1,2,3,4,5,6,7,8
   lpm r25, Z+
   mov r\i, r25
.endr

While Atmel Studio does highlight .irp (it doesn't other highlight everything that starts with a .) it doesn't work: Invalid directive: '.irp'

See also my other, related question: MOV into a register specified by macro argument.

Oh indeed! Why not copying register pairs (it takes only 1 cycle to copy 2 bytes): "lpm to r24", "lpm to r25", "load r0-r1 with r24-r25" ? — Egor Skriptunoff, Mar 15 '14 at 17:43
Sorry my pseudocode :) The correct instruction name is `movw` — Egor Skriptunoff, Mar 16 '14 at 15:27
And in the end you were right, I could in fact `lpm` into the lower registers as well, just not `ldi`. — Thom Wiggers, Mar 21 '14 at 15:23

score 1 · Answer 1 · answered Mar 14 '14 at 22:11

1

I know that this doesn't directly answer your question, but are you aware of the fact that AVR registers are memory mapped at address zero? So you could use a runtime memory copy loop instead of this macro construct. Unbeknownst to me, you might of course have some other constraints that rule this option out.

answered Mar 14 '14 at 22:11

Jester

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Jumps cost 2 cycles and I need to use as few cycles as possible. – Thom Wiggers Mar 15 '14 at 16:27
Yeah I was thinking something like that when I was talking about unknown constraints :) – Jester Mar 15 '14 at 16:30

How do I do this AVR assembly more elegantly

1 Answers1