py/asm*: Support assembling code to jump to a register, and get PC+off.

Useful for position independent code, and implementing state machines.

1 files changed, 9 insertions, 0 deletions

diff --git a/py/asmthumb.c b/py/asmthumb.c
index ce9e4fdce..6550d9398 100644
--- a/py/asmthumb.c
+++ b/py/asmthumb.c
@@ -310,6 +310,15 @@ void asm_thumb_mov_reg_local_addr(asm_thumb_t *as, uint rlo_dest, int local_num)
     asm_thumb_op16(as, OP_ADD_REG_SP_OFFSET(rlo_dest, word_offset));
 }
 
+void asm_thumb_mov_reg_pcrel(asm_thumb_t *as, uint rlo_dest, uint label) {
+    mp_uint_t dest = get_label_dest(as, label);
+    mp_int_t rel = dest - as->base.code_offset;
+    rel -= 4 + 4; // adjust for mov_reg_i16 and then PC+4 prefetch of add_reg_reg
+    rel |= 1; // to stay in Thumb state when jumping to this address
+    asm_thumb_mov_reg_i16(as, ASM_THUMB_OP_MOVW, rlo_dest, rel); // 4 bytes
+    asm_thumb_add_reg_reg(as, rlo_dest, ASM_THUMB_REG_R15); // 2 bytes
+}
+
 // this could be wrong, because it should have a range of +/- 16MiB...
 #define OP_BW_HI(byte_offset) (0xf000 | (((byte_offset) >> 12) & 0x07ff))
 #define OP_BW_LO(byte_offset) (0xb800 | (((byte_offset) >> 1) & 0x07ff))