Zigbee Network Processor (ZNP) Interface

1. Introduction

The Z-Stack Zigbee Network Processor (ZNP) is a cost-effective, low power solution that provides full Zigbee functionality with a minimal development effort.

In this solution, the Z-Stack runs on a SoC, i.e. the CC26x2 and the application runs on an external microcontroller, being any host processor. The Z-Stack ZNP handles all the Zigbee protocol tasks, and leaves the resources of the application microcontroller free to handle the application.

This makes it easy for users to add Zigbee to new or existing products at the same time as it provides great flexibility in choice of microcontroller.

Z-Stack ZNP interfaces to any microcontroller through a range of serial interfaces.

Figure 61. Single Device and ZNP Configuration

References

1. Z-Stack Monitor and Test API

Acronyms

AF	Zigbee Application Framework
API	Application Programming Interface
AREQ	Asynchronous Request
BDB	Base Device Behavior
CTS	Clear To Send
FCS	Frame Check Sequence
GP	Green Power
GPIO	General Purpose I/O
NPI	Network Processor Interface
NV	Non-Volatile
PA/LNA	Power Amplifier / Low Noise Amplifier (CC259x)
RTS	Ready To Send
SoC	System on Chip
SREQ	Synchronous request
SRSP	Synchronous response
UART	Universal Asynchronous Receiver Transmitter
ZDO	Zigbee Device Object
ZNP	Zigbee Network Processor

2. Physical Interface

The following sections describe the physical interfaces for the ZNP.

2.1 Network Processor Signals

The figure below shows how an application processor interfaces with the CC26x2.

The CC26x2 ZNP uses RX/TX/RTS/CTS for UART communication. See 2.2.4 Signal Description for details.

2.1.1 Pin Configurations

The CC26x2 ZNP pin configurations are described in the following sections.

Default Pin Configuration

By default, the pin configurations are the following:

Transport	CC26x2 ZNP signal	CC26x2 PIN	Direction
UART	TX	DIO_3	Out
UART	RX	DIO_2	In
UART	GND	GND	In/Out

Optional Pin Configuration

If NPI_FLOW_CTRL is enabled then the following pins also apply:

Transport	CC26x2 ZNP signal	CC26x2 PIN	Direction
UART	CTS	DIO_19	In
UART	RTS	DIO_18	Out

For additional information of different parameters which can be modified, refer to the Application Preprocessor Configuration.

2.2 UART Transport

2.2.1 Configuration

The following UART configuration is supported:

• Baud rate: 115200
• CTS/RTS flow control with NPI_FLOW_CTRL enabled (disabled by default)
• 8-N-1 byte format

2.2.2 Frame Format

UART transport frame format is shown in the following figure. The left-most field is transmitted first over the wire. This is the same General Serial Packet defined by the Z-Stack Monitor and Test API.

Table 1. UART Transport Frame Format

SOF	General Frame Format	FCS
Bytes: 1	3-253	1

SOF (Start of Frame): This is always set to 0xFE.

General Frame Format: This is the general frame format as described in 2.3 General Frame Format.

FCS (Frame Check Sequence): This field is computed as an XOR of all the bytes in the general format frame fields.

2.2.3 Sample FCS Calculation

Shown below is a C example for the FCS calculation:

unsigned char calcFCS(unsigned char *pMsg, unsigned char len)
{
  unsigned char result = 0;
  while (len--)
  {
    result ^= *pMsg++;
  }
  return result;
}

2.2.4 Signal Description

The following standard UART signals are used:

• TX: Transmit data
• RX: Receive data
• CTS: Clear to Send
• RTS: Ready to Send

Note

CTS/RTS are disabled by default, and are optional. You may enable CTS/RTS by defining NPI_FLOW_CTRL in the predefined symbols. For more information, refer to the Application Preprocessor Configuration.

The figure below shows the RTS/CTS flow control connections to the host processor. On the CC26x2, RTS and CTS are active-low signals. The RT output is driven low when the receive register is empty and reception is enabled. Transmission of a byte does not occur before the CTS input is low.

2.2.5 Signal Operation

UART transport sends and receives data asynchronously. Data can be sent and received simultaneously and the transfer of a frame can be initiated at any time by either the application processor or the ZNP SoC.

2.3 General Frame Format

The general frame format is shown in Table 2.. The left-most field is transmitted first over the wire. For multi-byte fields, the lowest order byte is transmitted first. This is the same General Frame Format defined by the Z-Stack Monitor and Test API.

Table 2. General Frame Format

Length	Command	Data
Bytes: 1	2	0-250

Length: The length of the data field of the frame. The length can range from 0-250.

Command: The Command ID for the message. Refer to 2.3.1 Command Field for more information about the Command field.

Data: The frame data. This field contains actual data to be transmitted. This depends on the command field and is described for each command in 3. ZNP Software Command Interface. The size can range from 0-250 bytes.

2.3.1 Command Field

The command field is constructed of two bytes. The bytes are formatted as shown in the following figure. The Cmd0 byte is transmitted first, followed by the Cmd1 byte.

Table 3. Command Field

Cmd0		Cmd1
Bit: 7-5	4-0	7-0
Type	Subsystem	Id

Type: The command type described by bits 5, 6, 7 of the Cmd0 byte. The command type has one of the following values:

Type	Cmd0 Value
POLL	0x00
SREQ	0x20
AREQ	0x40
SRSP	0x60

• 0: POLL. Not used in Z-Stack.
• 1: SREQ: A synchronous request that requires an immediate response. For example, a function call with a return value would use an SREQ command.
• 2: AREQ: An asynchronous request. For example, a callback event or a function call with no return value would use an AREQ command.
• 3: SRSP: A synchronous response. This type of command is only sent in response to a SREQ command. For an SRSP command the subsystem and ID are set to the same values as the corresponding SREQ. The length of an SRSP is generally nonzero, so an SRSP with length=0 can be used to indicate an error.
• 4-7: Reserved.

Subsystem: The subsystem of the command is described by bits 0-4 of Cmd0. The command subsystem values are shown below:

Subsystem Value	Subsystem Name
0x00	RPC Error interface
0x01	SYS interface
0x02	MAC interface
0x03	NWK interface
0x04	AF interface
0x05	ZDO interface
0x06	Simple API interface
0x07	UTIL interface
0x08	DEBUG interface
0x09	APP Interface
0x0F	APP config
0x15	GreenPower

ID: The command ID. The ID maps to a particular interface message.

Cmd1 provides an 8-bit command ID code, which maps to a specific interface message for the Subsystem specified in Cmd0. Therefore, each MT subsystem can provide up to 256 message handling functions.

3.3.2 Command Error

When an SREQ command from the Host Processor is not recognized by the ZNP, an error SRSP is returned, detailed in the two tables below.

SRSP:

Bytes: 1	1	1	1	1	1
Length = 0x03	Cmd0 = 0x60	Cmd1 = 0x00	ErrorCode	ReqCmd0	ReqCmd1

Attributes:

Attribute	Length (byte)	Description
ErrorCode	1	The error code maps to one of the following enumerated values. Value Description 0x01 Invalid subsystem 0x02 Invalid command ID 0x03 Invalid parameter 0x04 Invalid length
ReqCmd0	1	The Cmd0 value of the processed SREQ
ReqCmd1	1	The Cmd1 value of the processed SREQ

2.4 Initialization Procedures

2.4.1 CC26x2 ZNP Power-up Procedure

The recommended power-up procedure is as follows:

1. Application processor and CC26x2 power up.
2. The application processor initializes its UART interface.
3. The application processor receives the SYS_RESET_IND message.

The CC26x2 ZNP can be reset when the application processor sends a SYS_RESET_REQ message.

3. ZNP Software Command Interface

The ZNP software command interface is sub-divided into the following categories

• The SYS interface (MT_SYS) provides the application processor with a low level interface to the ZNP hardware and software.
• The AF (MT_AF) and ZDO (MT_ZDO) interfaces feature the complete Zigbee interface and can be used to create a full range of Zigbee compliant applications. The AF (Application Framework) interface allows the application processor to register its application with the ZNP and send and receive data. The ZDO (Zigbee Device Object) interface provides various Zigbee management functions like device and service discovery.
• The UTIL (MT_UTIL) interface provides support functionalities such as setting PAN-ID, getting device info, getting NV info, subscribing callbacks, etc.
• The APP CONF (MT_APP_CNF) interface provides support for BDB functionality such as set Install Codes, Primary or Secondary Channel, trigger different commissioning methods and other Trust Center configurations.

For further details on the MT interface, refer to the Z-Stack Monitor and Test API.

3.1 Configuration Interface

The ZNP device has numerous parameters that can be configured by the application processor. These configuration parameters are stored in non-volatile memory on the ZNP device and their values persist across a device reset.

The configuration parameters are divided into “network-specific” and “device-specific” parameters. The “network-specific” configuration parameters should be set to the same value for all ZNP devices in a Zigbee network to ensure proper network operation. The “device-specific” parameters can be set to different values on each device. These parameters are listed in detail in 3.1.1 Device Specific Configuration Parameters and 3.1.2 Network Specific Configuration Parameters. These configuration parameters must be written in NV for which the host processor must use the MT interface to write NV parameters into the ZNP device. Refer to the Z-Stack Monitor and Test API for further details on how to write into NV.

When the ZNP device powers up, it reads two of the configuration parameters immediately. These are the STARTOPT_CLEAR_CONFIG bit (part of the ZCD_NV_STARTUP_OPTION parameter) and the ZCD_NV_LOGICAL_TYPE parameters. Any modification of these parameters will require a ZNP device reset before they can take effect.

3.1.1 Device Specific Configuration Parameters

3.1.1.1 ZCD_NV_STARTUP_OPTION

Item ID	Size	Default Value
0x0003	1 Byte	0x00

This parameter controls the device startup options. This is a bit mask of the following values:

Bit Position	Description
7	ZCD_STARTOPT_CLEAR_NWK_FRAME_COUNTER
6-2	Reserved
1	ZCD_STARTOPT_CLEAR_STATE
0	ZCD_STARTOPT_CLEAR_CONFIG

• ZCD_STARTOPT_CLEAR_NWK_FRAME_COUNTER – If this option is set, then the network frame counter is cleared for all networks.

Note

This should be use only for debug purposes as the network frame counters must be persistant, even after Factory New resets. The usage of this option during the operation in the networks may lead to undesaried behaviour, such as get the ZNP device ignored by other devices in the network.

• ZCD_STARTOPT_CLEAR_CONFIG – If this option is set, the device will overwrite all the configuration parameters (except this one) with the “default” values that it is programmed with. This is used to erase the existing configuration and bring the device into a known state.

Note

The ZCD_STARTOPT_CLEAR_CONFIG bit is read by the ZNP device immediately when it powers up after a reset. When the configuration parameters are restored to defaults, the ZCD_NV_STARTUP_OPTION itself is not restored except for clearing the ZCD_STARTOPT_CLEAR_CONFIG bit.

• ZCD_STARTOPT_CLEAR_STATE – If this option is set, the device will clear its previous network state (which would exist if the device had been operating on a network prior to the reset). This is typically used during application development. During regular device operation, this flag is typically not set, so that an accidental device reset will not cause loss of network state.

The ZNP device has two kinds of information stored in non-volatile memory. The configuration parameters (in this section) and network state information (in 3.1.2 Network Specific Configuration Parameters)

The configuration parameters are configured by the user before start of Zigbee operation.

The network state information is collected by the device after it joins a network and creates bindings (at runtime). This is not set by the application processor. This information is stored so that if the device were to reset, it can restore itself without going through the network joining and binding process again.

If the application processor does not wish to continue operating in the previous Zigbee network, it needs to instruct the ZNP device to clear the network state information and start again based on the configuration parameters. This is done by setting the ZCD_STARTOPT_CLEAR_STATE bit in the startup option.

3.1.1.2 ZCD_NV_LOGICAL_TYPE

Item ID	Size	Default Value
0x0087	1 Byte	0x00

This is the logical type of the device in the Zigbee network. This can be set to a ZG_DEVICETYPE_COORDINATOR (0x00), ZG_DEVICETYPE_ROUTER (0x01), or ZG_DEVICETYPE_ENDDEVICE (0x02).

Note

This parameter is read by the ZNP device immediately when it powers up after a reset.

3.1.1.3 ZCD_NV_ZDO_DIRECT_CB

Item ID	Size	Default Value
0x008F	1 Byte	TRUE

This configures the manner in which ZDO responses (hereby referred to as callbacks) are issued to the host processor. By default, this item is set to TRUE, which means that the host processor will receive the “verbose” response. For example, the host processor would receive the ZDO_IEEE_ADDR_RSP command in response to ZDO_IEEE_ADDR_REQ. If ZCD_NV_ZDO_DIRECT_CB is set to FALSE, then the host processor must use the ZDO_MSG_CB_REGISTER command to subscribe to a specific ZDO callback in order to receive it.

3.1.2 Network Specific Configuration Parameters

3.1.2.1 ZCD_NV_PANID

Item ID	Size	Default Value
0x0083	2 Bytes	0xFFFF

This parameter identifies the Zigbee network. This should be set to a value between 0 and 0x3FFF. Networks that exist in the same vicinity must have different values for this parameter. It can be set to a special value of 0xFFFF to indicate “don’t care”.

3.2 Z-Stack 3.0 ZNP Considerations

3.2.1 Backward compatibility

ZNP is backward compatible with non Z3.0 devices by using the same API that already existed in previous releases of the Z-Stack, or by using Base Device Behavior commissioning MT interface with exception of the new security schemas for Z3.0 such as Distributed networks or Install Codes.

3.2.2 ZNP for Z3.0

While the ZNP implementation provides a compatible baseline for Zigbee 3.0 devices, a full implementation of a Zigbee 3.0 device involves additional layers on top of the ZNP. These layers shall be implemented by the user on the host-side of the stack, since they are outside the scope of the network processor. The ZNP provides several new interfaces to enable the required functionality on the host.

In order to update a legacy ZNP-based device to support Zigbee 3.0, the following main updates need to be implemented on the host:

Base Device Behavior Specification:

1. Finding and Binding: Host processor is required to implement Finding and Binding commissioning method (either as Initiator or as Target) according to the cluster supported by the host application.
2. Touchlink (optional): proximity-based commissioning method.

Green Power Basic Proxy:

Zigbee 3.0 coordinator and router devices must implement Green Power Basic proxy functionality. ZNP includes the necessary GP Stub interfaces which are available to the application and allow it to implement GP basic proxy functionality on the host processor.

3.2.3 ZNP Startup Procedure for Z3.0 Implementation

After executing the power-up procedure, the host processor must call some mandatory APIs before executing any APIs that invoke Zigbee over-the-air messaging. Not following this sequence could result in unexpected behaviour. The recommended startup procedure is as follows:

1. The host processor must use the ZB_WRITE_CONFIGURATION command to configure at the minimum the ZCD_NV_LOGICAL_TYPE.
2. If logical device is defined as ZC or ZR, GP basic proxy must be initialized in the host processor (No ZNP commands are required until interaction with GP devices are needed).
3. Optional configurations to commission the device are:

1. Set the Primary and/or Secondary channel mask to perform Formation or Network Steering.
2. Set the PAN ID to create or join by setting ZCD_NV_PAN_ID.
3. Set Install codes for networks which require it.

4. AF_REGISTER command should be sent by the host processor to register the application endpoint.
5. Host should use BDB commissioning API to create or join the network via standard network formation or joining.
6. The host processor should wait for BDB notifications on the different commissioning methods used by the host. Also host processor can rely on the supported ZDO states reported.

3.2.4 Example Message Exchange

The following sequence chart is provided as a simple example of a message exchange between a Host and ZNP. In this example the following (generalized) events take place:

Figure 62. Example Message Sequence Chart

3.3 Return Values

The status parameter that is returned from the ZNP device may take one of the following values:

Table 4. General Collection of Status Values

Name	Value
ZSuccess	0x00
ZFailure	0x01
ZInvalidParameter	0x02
ZDecodeError	0x03
NV_ITEM_UNINIT	0x09
NV_OPER_FAILED	0x0a
NV_BAD_ITEM_LEN	0x0c
ZMemError	0x10
ZBufferFull	0x11
ZUnsupportedMode	0x12
ZMacMemError	0x13
ZSapiInProgress	0x20
ZSapiTimeout	0x21
ZSapiInit	0x22
ZNotAuthorized	0x7E
ZMalformedCmd	0x80
ZUnsupClusterCmd	0x81
ZOtaAbort	0x95
ZOtaImageInvalid	0x96
ZOtaWaitForData	0x97
ZOtaNoImageAvailable	0x98
ZOtaRequireMoreImage	0x99
ZApsFail	0xb1
ZApsTableFull	0xb2
ZApsIllegalRequest	0xb3
ZApsInvalidBinding	0xb4
ZApsUnsupportedAttrib	0xb5
ZApsNotSupported	0xb6
ZApsNoAck	0xb7
ZApsDuplicateEntry	0xb8
ZApsNoBoundDevice	0xb9
ZApsNotAllowed	0xba
ZApsNotAuthenticated	0xbb
ZSecNoKey	0xa1
ZSecOldFrmCount	0xa2
ZSecMaxFrmCount	0xa3
ZSecCcmFail	0xa4
ZNwkInvalidParam	0xc1
ZNwkInvalidRequest	0xc2
ZNwkNotPermitted	0xc3
ZNwkStartupFailure	0xc4
ZNwkTableFull	0xc7
ZNwkUnknownDevice	0xc8
ZNwkUnsupportedAttribute	0xc9
ZNwkNoNetworks	0xca
ZNwkLeaveUnconfirmed	0xcb
ZNwkNoAck	0xcc
ZNwkNoRoute	0xcd
ZMacNoACK	0xe9
ZAfDuplicateEndpoint	0xd0
ZAfEndpointMax	0xd1
ZIcallNoMsg	0x30
ZIcallTimeout	0x31

Table 5. Common ZDO Status Values

Name	Value	Description
SUCCESS	0x00	Operation completed successfully
INVALID_REQTYPE	0x80	Supplied request type invalid
DEVICE_NOT_FOUND	0x81	Device not found
INVALID_EP	0x82	Invalid Endpoint value
NOT_ACTIVE	0x83	Endpoint not described by simple description
NOT_SUPPORTED	0x84	Optional feature not supported
TIMEOUT	0x85	Operation timed out
NO_MATCH	0x86	No match for End Device bind
NO_ENTRY	0x88	Unbind request failed, no entry
NO_DESCRIPTOR	0x89	Child descriptor not available
INSUFFICIENT_SPACE	0x8a	Insufficient space to support operation
NOT_PERMITTED	0x8b	Not in proper state to support operation
TABLE_FULL	0x8c	No table space to support operation
NOT_AUTHORIZED	0x8d	Permissions indicate request not authorized
BINDING_TABLE_FULL	0x8e	No binding table space to support operation

3.4 Additional Considerations for ZNP device in Z-Stack 3.0

1. The current version of ZNP device does not support commissioning GP devices in the network if these devices require the basic proxy device to switch channel during this commissioning process. Other commissioning methods require that a Host Processor drives the commissioning process in the application level.

3.5 Additional Information

For additional details of the individual commands, please refer to the Z-Stack Monitor and Test API.