Use atomic wait/notify on RXTAIL in KEY

emu.js

@@ -27,6 +27,7 @@ class Emulator {
 		this.mem_u8 = new Uint8Array(this.mem.buffer);
 		for (let i = 0; i < PERIPHS_SIZE; ++i)
 			this.mem_u8[i] = 0;
+		this.mem_i32 = new Int32Array(this.mem.buffer);
 
 		this.decoder = new TextDecoder('utf-8');
 		this.encoder = new TextEncoder('utf-8');
@@ -103,6 +104,7 @@ class Emulator {
 			tail = this.fifo_next(tail);
 		} while (this.fifo_next(tail) != head && this.rx_queue.length != 0);
 		Atomics.store(this.mem_u8, RXTAIL, tail);
+		Atomics.notify(this.mem_i32, RXTAIL / 4);
 	}
 
 	print(str) {

wipforth.wat

@@ -628,15 +628,24 @@
  ;; Serial I/O
 
  (func $key (local $head i32)
-       ;; Wait for RXBUF to be non-empty
-       loop $wait
        global.get $RXHEAD
        i32.atomic.load8_u
        local.tee $head
+
+       ;; Wait for RXBUF to be non-empty
+       loop $wait (param i32)
          global.get $RXTAIL
          i32.atomic.load8_u
          i32.eq
-         br_if $wait
+		 if
+		   global.get $RXTAIL
+		   local.get $head
+		   i64.const -1
+		   memory.atomic.wait32
+
+		   local.get $head
+		   br $wait
+		 end
        end
 
        ;; Read byte at head position