1 files changed, 29 insertions, 0 deletions
diff --git a/newasm/regreg.s b/newasm/regreg.s
new file mode 100644
index 0000000..6893dee
--- /dev/null
+++ b/newasm/regreg.s
@@ -0,0 +1,29 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.type regreg, %function
+.global regreg
+
+// R1 instruction under construction
+// R2 output buffer
+// R4 input buffer
+
+regreg:   PUSH    {LR}
+          BL      register    // parse a register
+          BNE     exit        // exit if failure
+          CMP     R2, 7       // check that it's R0-R7
+          BHI     bad_reg
+          ORRS    R1, R2      // fill in Rdn
+          BL      whitespace  // mandatory whitespace
+          BNE     exit        // exit if failure
+          BL      register    // parse a register
+          BNE     exit
+          CMP     R2, 7       // check that it's R0-R7
+          BHI     bad_reg
+          LSLS    R2, 3       // shift by 3
+          ORRS    R1, R2      // fill in Rm
+          MOVS    R0, 0       // return code 0 (success)
+exit:     POP     {PC}
+bad_reg:  MOVS    R0, 8       // return code 8 (invalid register for this register position)
+          POP     {PC}