diff --git a/atusb/fw/usb/usb.h b/atusb/fw/usb/usb.h
index 403d694..ff4dfe0 100644
--- a/atusb/fw/usb/usb.h
+++ b/atusb/fw/usb/usb.h
@@ -19,6 +19,20 @@
 #include <stdint.h>
 
 
+/*
+ * Packet identifier types
+ */
+
+#define	PID_OUT		0x1
+#define	PID_IN		0x9
+#define	PID_SOF		0x5
+#define	PID_SETUP	0xd
+#define	PID_DATA0	0x3
+#define	PID_DATA1	0xb
+#define	PID_ACK		0x2
+#define	PID_NAK		0xa
+#define	PID_STALL	0xe
+
 /*
  * Descriptor types
  *