Red Hat ENTERPRISE LINUX 4 Manual page 192

184
R
An item in the constant pool
S
A symbol in the text segment of the current file
AVR family--
avr.h
l
Registers from r0 to r15
a
Registers from r16 to r23
d
Registers from r16 to r31
w
Registers from r24 to r31. These registers can be used in
e
Pointer register (r26-r31)
b
Base pointer register (r28-r31)
q
Stack pointer register (SPH:SPL)
t
Temporary register r0
x
Register pair X (r27:r26)
y
Register pair Y (r29:r28)
z
Register pair Z (r31:r30)
I
Constant greater than -1, less than 64
J
Constant greater than -64, less than 1
Chapter 6. Extensions to the C Language Family
adiw
command