1 files changed, 40 insertions, 0 deletions
diff --git a/newasm/opcode.s b/newasm/opcode.s
new file mode 100644
index 0000000..71a5201
--- /dev/null
+++ b/newasm/opcode.s
@@ -0,0 +1,40 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.type opcode, %function
+.global opcode
+
+// 1 unexpected first char
+
+// R1 input buffer
+// R2 output buffer
+
+opcode:   PUSH    {LR}
+          LDRB    R0, [R1]    // get a char
+          CMP     R0, 0x41    // A
+          BLO     1f
+          CMP     R0, 0x5A    // Z
+          BLS     2f
+1:        MOVS    R0, #1      // unexpected char
+          POP     {PC}
+2:        ADDS    R1, 1       // consume the character
+          STRB    R0, [R2]    // store in temp buffer
+          ADDS    R2, 1       // advance temp buffer pointer
+          LDRB    R0, [R1]    // get another character
+          BL      goodchar    // check if valid symbol char
+          BEQ     2b          // if so keep getting chars
+          MOVS    R0, #0      // return code success
+          STRB    R0, [R2]    // write null byte
+          POP     {PC}
+
+goodchar: CMP     R0, '0
+          BLO     bad
+          CMP     R0, '9
+          BLS     good
+          CMP     R0, 'A
+          BLO     bad
+          CMP     R0, 'Z
+          BHI     bad
+good:     CMP     R0, R0
+bad:      BX      LR