FPGA Configuration

Introduction What is configuration? – Process for loading data into the FPGA Configuration Data Source Configuration Data Source FPGA Control Logic (optional) Control Logic (optional)

Introduction When does configuration happen? – On power-up – On demand Why do FPGAs need to be configured? – FPGA configuration memory is volatile What do I need to know about FPGA configuration? – What happens during configuration – How to set up various configuration modes and daisy-chains – How to troubleshoot problems

FPGA Configuration Process In order to understand the configuration process, you need to know a little about: – Configuration modes – Configuration pins

Configuration Modes Configuration modes define the specifics of how the FPGA will interact with: – The data source – External control logic (if any) Many configuration modes to choose from – Serial modes (Master and Slave) – SelectMAP mode (Slave Parallel) – Boundary scan mode (Slave) - always available – Other Xilinx FPGA families have more configuration modes

Configuration Modes Configuration pins ( M0, M1, M2) ) Note:

Data is loaded 1 bit per CCLK Master serial – FPGA drives configuration clock (CCLK) – FPGA provides all control logic Slave serial – External control logic required to generate CCLK Microprocessor Xilinx serial download cable Another FPGA Configuration Modes: Serial Modes Serial Data Serial Data FPGA CCLK Data Serial Data Serial Data FPGA Control Logic Control Logic Data CCLK

CCLK is driven by external logic Data is loaded 1 byte per CCLK Configuration Modes: SelectMAP Mode Byte-Wide Data Byte-Wide Data FPGA Control Logic Control Logic Data CCLK Control Signals

External control logic required Control signals and data are presented on the boundary scan pins (TDI, TMS, TCK) Data is loaded 1 bit per TCK Always available (independently on M0,M1,M2 ) Configuration Modes: Boundary Scan Mode Serial Data Serial Data FPGA Control Logic Control Logic Data Control Signals

Configuration Pins Specific pins on the FPGA are used during configuration Some pins act differently depending on configuration mode Example: CCLK is an output in some modes and an input in others Some pins are only used in specific configuration modes Example: CCLK is not used for Boundary Scan mode

Configuration Pin Descriptions Mode Pins (M0, M1, M2) Input pins that select which configuration mode is being used PROGRAM Active low input that initiates configuration CCLK (Configuration Clock) Input or output, depending on configuration mode Frequency up to 10MHz (see Data Book for your device family) DIN Serial input for configuration data

Configuration Pin Descriptions DOUT Output to next device in a daisy-chain Used in daisy-chains only INIT Open-drain bi-directional pin Error and Power Stabilization Flag DONE Open-drain bi-directional pin Indicates completion of configuration process Other pins are used for specific configuration modes (i.e. JTAG Pins)

Configuration Process Four major phases in the process: – Configuration memory clear – Initialization – Load configuration data – Start-up

Initialization Configuration Process Configuration Memory Clear Phase 2 Way to configure (power up - Program) Non-configuration I/O pins are disabled with optional pull-up resistors INIT and DONE pins are driven low FPGA memory is cleared – PROGRAM is checked after each memory pass Proceed to initialization

Configuration Memory Clear Load Configuration Data No Yes INIT High? Release INIT Sample Mode Pins Configuration Process: Initialization Phase INIT pin is released – INIT may be held low externally to delay configuration Mode pins are sampled – Appropriate configuration pins become active Proceed to load configuration data

Initialization Start-Up No Yes CRC Correct? Load Data Frames Pull INIT Low Configuration Process: Load Configuration Data Phase FPGA starts receiving data CRC is checked during the data frames transmission – If incorrect value received, INIT is driven low and rest of data is ignored If the CRC checks pass, proceed to start-up

Load Configuration Data FPGA is Operational Release DONE Activate I/O Pins Release GWE Release GSR Configuration Process: Start-up Phase Transition phase from configuration to normal operation Order of events is user programmable – Accessed through software options Default sequence is: – DONE pin is released – All I/O pins become active – Global write enable released – Global reset released FPGA is operational

Configuration Process: Start-up Phase Default sequence is: – DONE pin is released – All I/O pins become active – Global write enable released – Global reset released Another useful sequence is “Sync to DONE” – Useful for multiple FPGA configuration (Daisy chain) – Configuration option

Master Serial Mode All mode pins tied low FPGA drives CCLK as an output Data stream loaded 1 bit at a time Use when data stream is stored in a serial PROM

Slave Serial Mode All mode pins tied high FPGA receives CCLK as an input Data stream loaded 1 bit at a time Use with the xilinx serial download cable

What Is a Daisy-Chain? Multiple FPGAs connected in series for configuration – Allows configuration of many devices from a single data source – Minimal board traces First device in the chain can be in master serial or slave serial mode All other devices must be in slave serial mode

Daisy-Chain Question How do you think these FPGAs could be connected to form a Daisy-chain?

Daisy-Chain Answer Connect all PROGRAM, CCLK and DONE pins together Connect each DOUT to the DIN of next device Recommend connecting INIT pins, but not required

Creating a Daisy-Chain Connect PROGRAM pins – Required so that all FPGAs will reprogram together Connect CCLK pins – Required so that all FPGAs are synchronized with each other and with the configuration data Connect DONE pins – Required so that all FPGAs start-up together Connect each DOUT to the DIN of next device – Required to allow each FPGA to receive configuration data Connect INIT pins – Recommended to create a single error flag, but not required

How a Daisy-Chain Works First FPGA in the chain is configured first – Keeps DOUT high until its configuration memory is full – Then data is passed to the next device in the chain Start-up sequence occurs after all devices are configured – FPGA devices pause after internally releasing DONE, and continue when DONE externally goes high

Debugging Steps Use the Configuration Problem Solver to find the cause of the problem If this is a Daisy-chain, determine which device is failing before using the Configuration Problem Solver

Configuration Problem Solver What is it? – A web-based tool that guides you through the troubleshooting process – Created and maintained by Xilinx applications engineers who specialize in FPGA configuration Where is it? – Go to – Under Troubleshoot, click on FPGA Configuration How do I use it? – The problem solver presents you with questions – You answer each question – It presents you with the most probable causes and solutions

Configuration Problem Solver: Example

Debugging a Daisy-chain Step 1: Remove all but the first device from the board and try to configure. Debug any problems using the Configuration Problem Solver Step 2: Insert the next device and configure again, debugging any problems Step 3: Repeat step 2 until all devices configure successfully

Review Questions Which phase of the configuration process takes the most time? What is the main difference between the master serial and slave serial configuration modes?

Answers Which phase of the configuration process takes the most time? – The load configuration data phase takes the bulk of the configuration time What is the main difference between the master serial and slave serial configuration modes? – CCLK is an output in master serial, input in slave serial

Summary Field programmable devices are configured on power- up from an external data source The phases of the configuration process are: – Configuration memory clear – Initialization – Load configuration data – Start-up Master serial and slave serial are the simplest configuration modes

Summary Multiple FPGAs can be connected in series to form a configuration Daisy-chain Use the Configuration Problem Solver on the web to debug failed configurations