RapidIO II Intel® FPGA IP User Guide

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ID 683444
Date 9/28/2020
Public
Document Table of Contents
Document Table of Contents x
Product Discontinuance Notification 1. About the RapidIO II Intel® FPGA IP 2. Getting Started 3. Parameter Settings 4. Functional Description 5. Signals 6. Software Interface 7. Testbench 8. RapidIO II IP Core User Guide Archives 9. Document Revision History for the RapidIO II Intel® FPGA IP User Guide A. Initialization Sequence B. Differences Between RapidIO II IP Core and RapidIO IP Core
1. About the RapidIO II Intel® FPGA IP x
1.1. Features 1.2. Device Family Support 1.3. IP Core Verification 1.4. Performance and Resource Utilization 1.5. Device Speed Grades 1.6. Release Information
1.1. Features x
1.1.1. Supported Transactions
1.3. IP Core Verification x
1.3.1. Simulation Testing 1.3.2. Hardware Testing 1.3.3. Interoperability Testing
2. Getting Started x
2.1. Installing and Licensing Intel® FPGA IP Cores 2.2. Intel® FPGA IP Evaluation Mode 2.32.4. Generating IP Cores2.32.4. Generating IP Cores 2.32.4. Generating IP Cores2.32.4. Generating IP Cores 2.5. RapidIO II IP Core Testbench Files 2.6. Simulating IP Cores 2.7. Integrating Your IP Core in Your Design 2.8. Compiling the Full Design and Programming the FPGA 2.9. Instantiating Multiple RapidIO II IP Cores in V-series FPGA devices
2.32.4. Generating IP Cores2.32.4. Generating IP Cores x
2.3.1. IP Core Generation Output ( Intel® Quartus® Prime Pro Edition) 2.4.1. IP Core Generation Output ( Intel® Quartus® Prime Standard Edition)
2.32.4. Generating IP Cores2.32.4. Generating IP Cores x
2.3.1. IP Core Generation Output ( Intel® Quartus® Prime Pro Edition) 2.4.1. IP Core Generation Output ( Intel® Quartus® Prime Standard Edition)
2.6. Simulating IP Cores x
2.6.1. Simulating the Testbench with the ModelSim Simulator 2.6.2. Simulating the Testbench with the VCS Simulator 2.6.3. Simulating the Testbench with the NCSim Simulator 2.6.4. Simulating the Testbench with the Xcelium Parallel Simulator
2.7. Integrating Your IP Core in Your Design x
2.7.1. Dynamic Transceiver Reconfiguration Controller 2.7.2. Transceiver PHY Reset Controller 2.7.3. Transceiver Settings 2.7.4. Adding Transceiver Analog Settings for Arria V GZ and Stratix V Variations 2.7.5. External Transceiver PLL
3. Parameter Settings x
3.1. Physical Layer Settings 3.2. Transport Layer Settings 3.3. Logical Layer Settings 3.4. Capability Registers Settings 3.5. Command and Status Registers Settings 3.6. Error Management Registers Settings
3.1. Physical Layer Settings x
3.1.1. Mode Selection 3.1.2. Data Settings 3.1.3. Transceiver Settings
3.2. Transport Layer Settings x
3.2.1. Enable 16-Bit Device ID Width 3.2.2. Enable Avalon® -ST Pass-Through Interface 3.2.3. Disable Destination ID Checking
3.3. Logical Layer Settings x
3.3.1. Maintenance Module Settings 3.3.2. Doorbell Module Settings 3.3.3. I/O Master Module Settings 3.3.4. I/O Slave Module Settings
3.4. Capability Registers Settings x
3.4.1. Device Identity CAR 3.4.2. Device Information CAR 3.4.3. Assembly Identity CAR 3.4.4. Assembly Information CAR 3.4.5. Processing Element Features CAR 3.4.6. Switch Port Information CAR 3.4.7. Switch Route Table Destination ID Limit CAR 3.4.8. Data Streaming Information CAR 3.4.9. Source Operations CAR 3.4.10. Destination Operations CAR
3.5. Command and Status Registers Settings x
3.5.1. Data Streaming Logical Layer Control CSR 3.5.2. Port General Control CSR 3.5.3. Port 0 Control CSR 3.5.4. Lane n Status 0 CSR 3.5.5. Extended Features Pointer CSR
4. Functional Description x
4.1. Interfaces 4.2. Clocking and Reset Structure 4.3. Logical Layer Interfaces 4.4. Transport Layer 4.5. Physical Layer 4.6. Error Detection and Management
4.1. Interfaces x
4.1.1. Avalon® -MM Master and Slave Interfaces 4.1.2. Avalon-ST Interface 4.1.3. RapidIO Interface
4.2. Clocking and Reset Structure x
4.2.1. Avalon System Clock 4.2.2. Reference Clock 4.2.3. Recovered Data Clock 4.2.4. Clock Rate Relationships in the RapidIO II IP Core 4.2.5. Clock Domains in Your Platform Designer System 4.2.6. Reset for RapidIO II IP Cores
4.3. Logical Layer Interfaces x
4.3.1. Register Access Interface 4.3.2. Input/Output Logical Layer Modules 4.3.3. Maintenance Module 4.3.4. Doorbell Module 4.3.5. Avalon-ST Pass-Through Interface
4.3.1. Register Access Interface x
4.3.1.1. Non-Doorbell Register Access Operations 4.3.1.2. Register Access Interface Signals
4.3.2. Input/Output Logical Layer Modules x
4.3.2.1. Input/Output Avalon-MM Master Module 4.3.2.2. Input/Output Avalon-MM Slave Module 4.3.2.3. Avalon® -MM Burstcount and Byteenable Encoding in RapidIO Packets 4.3.2.4. Input/Output Avalon® -MM Slave Module Timing Diagrams
4.3.2.1. Input/Output Avalon-MM Master Module x
4.3.2.1.1. Input/Output Avalon-MM Master Interface Signals 4.3.2.1.2. Defining the Input/Output Avalon-MM Master Address Mapping Windows 4.3.2.1.3. RapidIO Packet Data Word Pointer and Size Encoding in Avalon® -MM Transactions 4.3.2.1.4. Input/Output Avalon-MM Master Module Timing Diagrams
4.3.2.2. Input/Output Avalon-MM Slave Module x
4.3.2.2.1. Input/Output Avalon-MM Slave Interface Signals 4.3.2.2.2. Initiating Read and Write Transactions 4.3.2.2.3. Defining the Input/Output Avalon-MM Slave Address Mapping Windows 4.3.2.2.4. Input/Output Slave Translation Window Example
4.3.3. Maintenance Module x
4.3.3.1. Maintenance Interface Transactions 4.3.3.2. Maintenance Interface Signals 4.3.3.3. Initiating MAINTENANCE Read and Write Transactions 4.3.3.4. Defining the Maintenance Address Translation Windows 4.3.3.5. Responding to MAINTENANCE Read and Write Requests 4.3.3.6. Handling Port-Write Transactions 4.3.3.7. Maintenance Interface Transaction Examples 4.3.3.8. Maintenance Packet Error Handling
4.3.3.3. Initiating MAINTENANCE Read and Write Transactions x
4.3.3.3.1. IP Core Actions
4.3.3.5. Responding to MAINTENANCE Read and Write Requests x
4.3.3.5.1. IP Core Actions
4.3.3.6. Handling Port-Write Transactions x
4.3.3.6.1. IP Core Actions 4.3.3.6.2. Port-Write Transmission 4.3.3.6.3. Port-Write Reception
4.3.3.7. Maintenance Interface Transaction Examples x
4.3.3.7.1. User Sending MAINTENANCE Write Requests 4.3.3.7.2. User Receiving MAINTENANCE Write Requests 4.3.3.7.3. User Sending MAINTENANCE Read Requests and Receiving Responses 4.3.3.7.4. User Receiving MAINTENANCE Read Requests and Sending Responses
4.3.4. Doorbell Module x
4.3.4.1. Preserving Transaction Order 4.3.4.2. Doorbell Module Interface Signals 4.3.4.3. Generating a Doorbell Message 4.3.4.4. Response to a DOORBELL Request 4.3.4.5. Receiving a Doorbell Message
4.3.5. Avalon-ST Pass-Through Interface x
4.3.5.1. Transaction ID Ranges 4.3.5.2. Pass-Through Interface Signals 4.3.5.3. Pass-Through Interface Usage Examples
4.3.5.3. Pass-Through Interface Usage Examples x
4.3.5.3.1. User Sending Write Request 4.3.5.3.2. User Receiving Write Request 4.3.5.3.3. User Sending Read Request and Receiving Read Response 4.3.5.3.4. User Receiving Read Request and Sending Read Response 4.3.5.3.5. User Sending Streaming Write Request 4.3.5.3.6. User Receiving Streaming Write Request
4.4. Transport Layer x
4.4.1. Receiver 4.4.2. Transmitter
4.5. Physical Layer x
4.5.1. Low-level Interface Receiver 4.5.2. Low-Level Interface Transmitter
4.6. Error Detection and Management x
4.6.1. Physical Layer Error Management 4.6.2. Logical Layer Error Management 4.6.3. Avalon-ST Pass-Through Interface
4.6.1. Physical Layer Error Management x
4.6.1.1. Protocol Violations 4.6.1.2. Fatal Errors
4.6.2. Logical Layer Error Management x
4.6.2.1. Maintenance Avalon-MM Slave 4.6.2.2. Maintenance Avalon-MM Master 4.6.2.3. Port-Write Reception Module 4.6.2.4. Port-Write Transmission Module 4.6.2.5. Input/Output Avalon-MM Slave 4.6.2.6. Input/Output Avalon-MM Master
5. Signals x
5.1. Global Signals 5.2. Physical Layer Signals 5.3. Logical and Transport Layer Signals 5.4. Error Management Extension Signals
5.2. Physical Layer Signals x
5.2.1. Status Packet and Error Monitoring Signals 5.2.2. Low Latency Signals 5.2.3. Transceiver Signals 5.2.4. Register-Related Signals
5.2.2. Low Latency Signals x
5.2.2.1. Multicast Event Signals 5.2.2.2. Link-Request Reset-Device Signals
5.3. Logical and Transport Layer Signals x
5.3.1. Avalon-MM Interface Signals 5.3.2. Avalon® -ST Pass-Through Interface Signals 5.3.3. Data Streaming Support Signals 5.3.4. Transport Layer Packet and Error Monitoring Signal
5.3.1. Avalon-MM Interface Signals x
5.3.1.1. Register Access Interface Signals 5.3.1.2. Input/Output Avalon-MM Master Interface Signals 5.3.1.3. Input/Output Avalon-MM Slave Interface Signals 5.3.1.4. Maintenance Interface Signals 5.3.1.5. Doorbell Module Interface Signals
5.4. Error Management Extension Signals x
5.4.1. Error Reporting Signals
6. Software Interface x
6.1. Memory Map 6.2. Physical Layer Registers 6.3. Transport and Logical Layer Registers
6.1. Memory Map x
6.1.1. CAR Memory Map 6.1.2. CSR Memory Map 6.1.3. LP-Serial Extended Features Block Memory Map 6.1.4. LP-Serial Lane Extended Features Block Memory Map 6.1.5. Error Management Extensions Extended Features Block Memory Map 6.1.6. Maintenance Module Registers Memory Map 6.1.7. I/O Logical Layer Master Module Registers Memory Map 6.1.8. I/O Logical Layer Slave Module Registers Memory Map 6.1.9. Doorbell Module Registers Memory Map
6.2. Physical Layer Registers x
6.2.1. LP-Serial Extended Features Block Memory Map 6.2.2. LP-Serial Lane Extended Features Block Memory Map
6.2.1. LP-Serial Extended Features Block Memory Map x
6.2.1.1. LP-Serial Register Block Header 6.2.1.2. Port Link Time-out Control CSR 6.2.1.3. Port Response Time-out Control CSR 6.2.1.4. Port General Control CSR 6.2.1.5. Port 0 Link Maintenance Request CSR 6.2.1.6. Port 0 Link Maintenance Response CSR 6.2.1.7. Port 0 Local AckID CSR 6.2.1.8. Port 0 Control 2 CSR 6.2.1.9. Port 0 Error and Status CSR 6.2.1.10. Port 0 Control CSR
6.2.2. LP-Serial Lane Extended Features Block Memory Map x
6.2.2.1. LP-Serial Lane Register Block Header 6.2.2.2. LP-Serial Lane n Status 0 6.2.2.3. LP-Serial Lane n Status 1 6.2.2.4. LP-Serial Lane n Status 2 6.2.2.5. LP-Serial Lane n Status 3 6.2.2.6. LP-Serial Lane n Status 4
6.3. Transport and Logical Layer Registers x
6.3.1. Capability Registers (CARs) 6.3.2. Command and Status Registers (CSRs) 6.3.3. Maintenance Module Registers 6.3.4. I/O Logical Layer Master Module Registers 6.3.5. I/O Logical Layer Slave Module Registers 6.3.6. Error Management Registers 6.3.7. Doorbell Message Registers
6.3.1. Capability Registers (CARs) x
6.3.1.1. CAR Memory Map 6.3.1.2. Device Identity CAR 6.3.1.3. Device Information CAR 6.3.1.4. Assembly Identity CAR 6.3.1.5. Assembly Information CAR 6.3.1.6. Processing Element Features CAR 6.3.1.7. Switch Port Information CAR 6.3.1.8. Source Operations CAR 6.3.1.9. Destination Operations CAR 6.3.1.10. Switch Route Table Destination ID Limit CAR 6.3.1.11. Data Streaming Information CAR
6.3.2. Command and Status Registers (CSRs) x
6.3.2.1. CSR Memory Map 6.3.2.2. Data Streaming Logical Layer Control CSR 6.3.2.3. Processing Element Logical Layer Control CSR 6.3.2.4. Local Configuration Space Base Address 0 CSR 6.3.2.5. Local Configuration Space Base Address 1 CSR 6.3.2.6. Base Device ID CSR 6.3.2.7. Host Base Device ID Lock CSR 6.3.2.8. Component Tag CSR
6.3.3. Maintenance Module Registers x
6.3.3.1. Maintenance Module Registers Memory Map 6.3.3.2. Maintenance Interrupt Control Registers 6.3.3.3. Transmit Maintenance Registers 6.3.3.4. Transmit Port-Write Registers 6.3.3.5. Receive Port-Write Registers
6.3.4. I/O Logical Layer Master Module Registers x
6.3.4.1. I/O Logical Layer Master Module Registers Memory Map 6.3.4.2. I/O Master Address Mapping Registers 6.3.4.3. I/O Master Interrupts
6.3.5. I/O Logical Layer Slave Module Registers x
6.3.5.1. I/O Logical Layer Slave Module Registers Memory Map 6.3.5.2. I/O Slave Address Mapping Registers 6.3.5.3. I/O Slave Interrupts 6.3.5.4. I/O Slave Transactions and Requests
6.3.6. Error Management Registers x
6.3.6.1. Error Management Extensions Extended Features Block Memory Map 6.3.6.2. Error Management Extensions Block Header 6.3.6.3. Logical/Transport Layer Error Detect 6.3.6.4. Logical/Transport Layer Error Enable 6.3.6.5. Logical/Transport Layer Address Capture 6.3.6.6. Logical/Transport Layer Device ID Capture 6.3.6.7. Logical/Transport Layer Control Capture 6.3.6.8. Port-Write Target Device ID 6.3.6.9. Packet Time-to-Live 6.3.6.10. Port 0 Error Detect 6.3.6.11. Port 0 Error Rate Enable 6.3.6.12. Port 0 Attributes Capture 6.3.6.13. Port 0 Packet/Control Symbol Capture 0 6.3.6.14. Port 0 Packet Capture 1 6.3.6.15. Port 0 Packet Capture 2 6.3.6.16. Port 0 Packet Capture 3 6.3.6.17. Port 0 Error Rate 6.3.6.18. Port 0 Error Rate Threshold
6.3.7. Doorbell Message Registers x
6.3.7.1. Doorbell Module Registers Memory Map 6.3.7.2. Rx Doorbell 6.3.7.3. Tx Doorbell 6.3.7.4. Doorbell Interrupt
7. Testbench x
7.1. Testbench Overview 7.2. Testbench Sequence 7.3. Testbench Completion 7.4. Transceiver Level Connections in the Testbench
7.2. Testbench Sequence x
7.2.1. Reset, Initialization, and Configuration 7.2.2. Maintenance Write and Read Transactions 7.2.3. SWRITE Transactions 7.2.4. NREAD Transactions 7.2.5. NWRITE_R Transactions 7.2.6. NWRITE Transactions 7.2.7. Doorbell Transactions 7.2.8. Port-Write Transactions 7.2.9. Transactions Across the AVST Pass-Through Interface
Product Discontinuance Notification
1. About the RapidIO II Intel® FPGA IP
2. Getting Started
3. Parameter Settings
4. Functional Description
5. Signals
6. Software Interface
7. Testbench
8. RapidIO II IP Core User Guide Archives
9. Document Revision History for the RapidIO II Intel® FPGA IP User Guide
A. Initialization Sequence
B. Differences Between RapidIO II IP Core and RapidIO IP Core

4.3.2.1.3. RapidIO Packet Data Word Pointer and Size Encoding in Avalon® -MM Transactions

The RapidIO II IP core converts RapidIO packets to Avalon® -MM transactions. The RapidIO packet's read size, write size, and word pointer fields, and the least significant bit of the address field, are translated to the Avalon® -MM burst count and byteenable values.

Table 15.   Avalon® -MM I/O Master Read Transaction Burstcount and Byteenable
RapidIO Field Values Avalon® -MM Signal Values
rdsize (4'bxxxx) wdptr (1'bx) address[0] (1'bx) Burstcount Byteenable (16'bxxxxxxxxxxxxxxxx)
0000 0 0 1 0000_0000_1000_0000
0 1 1 1000_0000_0000_0000
1 0 1 0000_0000_0000_1000
1 1 1 0000_1000_0000_0000
0001 0 0 1 0000_0000_0100_0000
0 1 1 0100_0000_0000_0000
1 0 1 0000_0000_0000_0100
1 1 1 0000_0100_0000_0000
0010 0 0 1 0000_0000_0010_0000
0 1 1 0010_0000_0000_0000
1 0 1 0000_0000_0000_0010
1 1 1 0000_0010_0000_0000
0011 0 0 1 0000_0000_0001_0000
0 1 1 0001_0000_0000_0000
1 0 1 0000_0000_0000_0001
1 1 1 0000_0001_0000_0000
0100 0 0 1 0000_0000_1100_0000
0 1 1 1100_0000_0000_0000
1 0 1 0000_0000_0000_1100
1 1 1 0000_1100_0000_0000
0101 13 0 0 1 0000_0000_1110_0000
0 1 1 1110_0000_0000_0000
1 0 1 0000_0000_0000_0111
1 1 1 0000_0111_0000_0000
0110 0 0 1 0000_0000_0011_0000
0 1 1 0011_0000_0000_0000
1 0 1 0000_0000_0000_0011
1 1 1 0000_0011_0000_0000
011113 0 0 1 0000_0000_1111_1000
0 1 1 1111_1000_0000_0000
1 0 1 0000_0000_0001_1111
1 1 1 0001_1111_0000_0000
1000 0 0 1 0000_0000_1111_0000
0 1 1 1111_0000_0000_0000
1 0 1 0000_0000_0000_1111
1 1 1 0000_1111_0000_0000
100113 0 0 1 0000_0000_1111_1100
0 1 1 1111_1100_0000_0000
1 0 1 0000_0000_0011_1111
1 1 1 0011_1111_0000_0000
101013 0 0 1 0000_0000_1111_1110
0 1 1 0000_0000_0111_1111
1 0 1 1111_1110_0000_0000
1 1 1 0111_1111_0000_0000
1011 0 0 1 0000_0000_1111_1111
0 1 1 1111_1111_0000_0000
1 0 1 1111_1111_1111_1111
1 1 Reserved14
1100 15 0 0 2 1111_1111_1111_1111
1 0 4 1111_1111_1111_1111
110115 0 0 6 1111_1111_1111_1111
1 0 8 1111_1111_1111_1111
111015 0 0 10 1111_1111_1111_1111
1 0 12 1111_1111_1111_1111
111115 0 0 14 1111_1111_1111_1111
1 0 16 1111_1111_1111_1111
Table 16.   Avalon® -MM I/O Master Write Transaction Burstcount and Byteenable IFor wrsize value less than 4’b1100:
RapidIO Field Values Avalon® -MM Signal Values
wrsize (4'bxxxx) wdptr (1'bx) address[0] (1'bx) Burstcount Byteenable (16'bxxxx_xxxx_xxxx_xxxx)
0000 0 0 1 0000_0000_1000_0000
0 1 1 1000_0000_0000_0000
1 0 1 0000_0000_0000_1000
1 1 1 0000_1000_0000_0000
0001 0 0 1 0000_0000_0100_0000
0 1 1 0100_0000_0000_0000
1 0 1 0000_0000_0000_0100
1 1 1 0000_0100_0000_0000
0010 0 0 1 0000_0000_0010_0000
0 1 1 0010_0000_0000_0000
1 0 1 0000_0000_0000_0010
1 1 1 0000_0010_0000_0000
0011 0 0 1 0000_0000_0001_0000
0 1 1 0001_0000_0000_0000
1 0 1 0000_0000_0000_0001
1 1 1 0000_0001_0000_0000
0100 0 0 1 0000_0000_1100_0000
0 1 1 1100_0000_0000_0000
1 0 1 0000_0000_0000_1100
1 1 1 0000_1100_0000_0000
0101 16 0 0 1 0000_0000_1110_0000
0 1 1 0000_0000_0000_0111
1 0 1 1110_0000_0000_0000
1 1 1 0000_0111_0000_0000
0110 0 0 1 0000_0000_0011_0000
0 1 1 0000_0000_0000_0011
1 0 1 0011_0000_0000_0000
1 1 1 0000_0011_0000_0000
011116 0 0 1 0000_0000_1111_1000
0 1 1 0000_0000_0001_1111
1 0 1 1111_1000_0000_0000
1 1 1 0001_1111_0000_0000
1000 0 0 1 0000_0000_1111_0000
0 1 1 1111_0000_0000_0000
1 0 1 0000_0000_0000_1111
1 1 1 0000_1111_0000_0000
100116 0 0 1 0000_0000_1111_1100
0 1 1 0000_0000_0011_1111
1 0 1 1111_1100_0000_0000
1 1 1 0011_1111_0000_0000
101016 0 0 1 0000_0000_1111_1110
0 1 1 0000_0000_0111_1111
1 0 1 1111_1110_0000_0000
1 1 1 0111_1111_0000_0000
1011 0 0 1 0000_0000_1111_1111
0 1 1 1111_1111_0000_0000
1 0 1 1111_1111_1111_1111
1 1 2

First clock cycle: 1111_1111_0000_0000

Second clock cycle: 0000_0000_1111_1111
Table 17.   Avalon® -MM I/O Master Write Transaction Burstcount and Byteenable IIFor wrsize value greater than 4’b1011:
RapidIO Values Avalon® -MM Signal Values
RapidIO Field Values Payload Size is Multiple of 16 Bytes17 Burstcount Byteenable (16'hXXXX)
wrsize (4'bxxxx) address[0] (1'bx) First Cycle Intermediate Cycles Final Cycle
1100–1111 0 Yes Payload size in bytes / 16 FFFF FFFF FFFF
1 Yes Payload size in bytes / 16 plus 1 FF00 FFFF 00FF
0 No 18 FFFF FFFF 00FF
1 No 18 FF00 FFFF FFFF
13 The RapidIO link partner should avoid read requests with this rdsize value, because the resulting byteenable value is not allowed by the Avalon® -MM specification. However, if the RapidIO II IP core receives a read request with this rdsize value, the IP core issues these transactions on the I/O Logical layer Avalon® -MM master interface with the illegal byteenable values, to support systems in which user logic handles these byteenable values.
14 This combination of wdptr and rdsize values is reserved. If the RapidIO II IP core receives this combination, it sets the Unsupported Transaction bit (UNSUPPORT_TRAN) in the Logical/Transport Layer Error Detect CSR and returns an ERROR response.
15 If rdsize has a value greater than 4’b1011, and address[0] has the value of 1, the RapidIO II IP core sets the Unsupported Transaction bit (UNSUPPORT_TRAN) in the Logical/Transport Layer Error Detect CSR and returns an ERROR response.
16 The RapidIO link partner should avoid this combination of wdptr and wrsize values, because the resulting byteenable value presented on the Avalon® -MM master interface is not allowed by the Avalon® -MM specification.
17 If the packet payload is larger than the maximum size allowed for the packet wrsize and wdptr values, the RapidIO II IP core records an Illegal transaction decode error in the Error Management Extension registers and, for NWRITE_R request packets, returns an ERROR response.
18 If the payload size is not a multiple of 16 bytes, and address[0] has the value of zero, the value of burstcount is the number of 8-byte words in the packet payload, divided by two, and rounded up.
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