AVR R0 to R15

How on earth do I access R0 to R15 of the general purpose registers? Whenever I try I get an error called invalid register...

Where could I have gone wrong...

Please excuse me if the question is dumb and help me out.

Thank You.

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Added a few minutes later:

Okay, I discovered that the instruction LDS to load into all 32 registers but the con is that it is a 2 word instruction unlike the ldi which is a single word instruction.

If anyone has anything to add that might clear any misconception that I have, please do so.

LDI only works on the upper 16 registers - R16-R31. There is no way of loading the lower 16 registers directly (I guess they ran out of instruction bits).

When doing assembly code, I usually leave the lower 16 registers for use as global state/temporaries

It is the case that there are not enough bits in the instruction word to allow ldi for all 32 registers. Write a two instruction sequence with a macro that does an ldi to R16 and then moves R16 to another register.