py: Add inline Xtensa assembler.

This patch adds the MICROPY_EMIT_INLINE_XTENSA option, which, when
enabled, allows the @micropython.asm_xtensa decorator to be used.

The following opcodes are currently supported (ax is a register, a0-a15):

    ret_n()
    callx0(ax)
    j(label)
    jx(ax)

    beqz(ax, label)
    bnez(ax, label)
    mov(ax, ay)
    movi(ax, imm) # imm can be full 32-bit, uses l32r if needed

    and_(ax, ay, az)
    or_(ax, ay, az)
    xor(ax, ay, az)
    add(ax, ay, az)
    sub(ax, ay, az)
    mull(ax, ay, az)

    l8ui(ax, ay, imm)
    l16ui(ax, ay, imm)
    l32i(ax, ay, imm)
    s8i(ax, ay, imm)
    s16i(ax, ay, imm)
    s32i(ax, ay, imm)
    l16si(ax, ay, imm)
    addi(ax, ay, imm)

    ball(ax, ay, label)
    bany(ax, ay, label)
    bbc(ax, ay, label)
    bbs(ax, ay, label)
    beq(ax, ay, label)
    bge(ax, ay, label)
    bgeu(ax, ay, label)
    blt(ax, ay, label)
    bnall(ax, ay, label)
    bne(ax, ay, label)
    bnone(ax, ay, label)

Upon entry to the assembly function the registers a0, a12, a13, a14 are
pushed to the stack and the stack pointer (a1) decreased by 16.  Upon
exit, these registers and the stack pointer are restored, and ret.n is
executed to return to the caller (caller address is in a0).

Note that the ABI for the Xtensa emitters is non-windowing.

1 files changed, 3 insertions, 0 deletions

diff --git a/py/compile.c b/py/compile.c
index b85e659e7..6c9b6abfe 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -91,6 +91,9 @@ typedef enum {
 #if MICROPY_EMIT_INLINE_THUMB
 #define ASM_DECORATOR_QSTR MP_QSTR_asm_thumb
 #define ASM_EMITTER(f) emit_inline_thumb_##f
+#elif MICROPY_EMIT_INLINE_XTENSA
+#define ASM_DECORATOR_QSTR MP_QSTR_asm_xtensa
+#define ASM_EMITTER(f) emit_inline_xtensa_##f
 #else
 #error "unknown asm emitter"
 #endif