Chapter 42. Xtensa Dependent Features

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The

L8UI

machine instruction can only be used with immediate offsets in the range from 0 to 255.

The

L16SI

and

L16UI

machine instructions can only be used with offsets from 0 to 510. The

L32I

machine instruction can only be used with offsets from 0 to 1020. A load offset outside these ranges

can be materalized with an

L32R

instruction if the destination register of the load is different than the

source address register. For example:

l32i a1, a0, 2040

is translated to:

.literal .L1, 2040

l32r a1, .L1

addi a1, a0, a1

l32i a1, a1, 0

If the load destination and source address register are the same, an out of range offset causes an error.

The Xtensa

ADDI

instruction only allows immediate operands in the range from  128 to 127. There

are a number of alternate instruction sequences for the generic

ADDI

operation. First, if the immediate

is 0, the

ADDI

will be turned into a

MOV.N

instruction (or the equivalent

OR

instruction if the code

density option is not available). If the

ADDI

immediate is outside of the range  128 to 127, but inside

the range  32896 to 32639, an

ADDMI

instruction or

ADDMI

/

ADDI

sequence will be used. Finally, if the

immediate is outside of this range and a free register is available, an

L32R

/

ADD

sequence will be used

with a literal allocated from the literal pool.

For example:

addi

a5, a6, 0

addi

a5, a6, 512

addi

a5, a6, 513

addi

a5, a6, 50000

is assembled into the following:

.literal .L1, 50000

mov.n

a5, a6

addmi

a5, a6, 0x200

addmi

a5, a6, 0x200

addi

a5, a5, 1

l32r

a5, .L1

add

a5, a6, a5

42.5. Directives

The Xtensa assember supports a region based directive syntax:

.begin directive [options]

...

.end directive