Cypress CY4672 manual Chip Error Correction, Automatic Acknowledgment AutoACK, Network ID

WirelessUSB™ Protocol 2.2

accommodate hundreds of WirelessUSB devices in the same space. Each bridge/HID pair must use the same PN code and channel in order to communicate with each other.

2.1.3Chip Error Correction

In the presence of interference (or near the limits of range), the transmitted PN code will often be received with some PN code chips corrupted. DSSS receivers use a data correlator to decode the incoming data stream. WirelessUSB LP supports a separate start of packet (SOP) and data thresh- old. The RDK uses an SOP threshold of ‘4’. The data threshold is set to the default value of ‘4’.

2.1.4Automatic Acknowledgment (AutoACK)

The WirelessUSB LP radio contains an automatic acknowledgment feature that allows it to automat- ically send an ACK to any valid packet that is received. The WirelessUSB LP radio also uses the concept of transactions to allow the radio in the HID to automatically power down after transmitting a packet and receiving an AutoACK instead of waiting for the firmware to power the radio down. This conserves power and reduces the firmware complexity of WirelessUSB applications.

2.1.5Network ID

The network ID contains the parameters for the channel selection algorithm as well as the PN code to be used. HIDs retrieve the network ID information from the bridge during the bind procedure. A special network ID is reserved for bind mode, known as the bind ID. The bind ID gives a common channel subset so that any two devices can communicate with each other during bind mode. The network ID is composed of the following fields:

PIN	This is a random number between 2–5 that defines the channel subset and is
	used in the channel selection algorithm.
Base Channel	This is the first channel to be used in the channel selection algorithm, that deter-
	mines which channels are contained in the channel subset.
PN Code	This is used as an index to select one of 10 used SOP PN codes, as noted in the
	radio driver document.
CRC Seed	This 8-bit value is used for the CRC calculation, that further diversifies transmis-
	sions from different networks. All packets sent between non-bound devices use
	the default CRC seed of 0x0000. All packets sent between bound devices use a
	CRC seed that is common to all devices bound to a particular bridge or network
	but unique from network to network.

2.1.6Manufacturing ID

Each WirelessUSB radio contains a 4-byte manufacturing ID (MID), that has been laser fused into the device during manufacturing. The bridge uses its MID to help randomize channel subsets, PN codes and network CRC seeds. The bridge sends its MID to the HIDs when binding. The HID then stores the bridge’s MID in non-volatile memory after binding. The HID sends the bridge’s MID as part of the connect request packet, allowing the bridge to verify the identity of the HID when establishing a connection.

Both the bridge and the HID use the bridge’s MID as to generate the device network ID components. The following equations ensure that each network will have a unique set of network ID components:

PN Code = [(mid_1 << 2) + mid_2 + mid_3] mod 10

Base Channel = [(mid_2 >> 2) – (mid_1 << 5) + mid_3] mod 78 PIN = [(((mid_1 -mid_2) & PIN_MASK) + MIN_PIN)] mod 78 CRC Seed = ((mid_2 >> 6)) + mid_1 + mid_3 if=0 then Seed = 1

14 CY4672 Reference Design Guide, Document # 001-16968 Revision **

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