micropython/docs/reference/asm_thumb2_stack.rst

Stack push and pop
==================

Document conventions
--------------------

The ``push()`` and ``pop()`` instructions accept as their argument a register set containing
a subset, or possibly all, of the general-purpose registers R0-R12 and the link register (lr or R14).
As with any Python set the order in which the registers are specified is immaterial. Thus the
in the following example the pop() instruction would restore R1, R7 and R8 to their contents prior
to the push():

* push({r1, r8, r7}) Save three registers on the stack.
* pop({r7, r1, r8}) Restore them

Stack operations
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* push({regset}) Push a set of registers onto the stack
* pop({regset}) Restore a set of registers from the stack