Answers Database Configuration: Dynamic Re-ordering of Daisy-Chain configurations. Record #3017 Product Family: Documentation Product Line: FPGA Apps. Product Part: FPGA Configuration Guidelines Problem Title: Configuration: Dynamic Re-ordering of Daisy-Chain configurations. Problem Description: Urgency: Standard General Description: For applications that need to choose the order of a daisy-chain configuration `on-the-fly' or reduce the amount of memory space needed to hold mutiple daisy-chain configuration streams, some manual intervention may be applied so that each FPGA copnfiguration need only be stored once. For example: A daisy-chain of 6 devices and multiple designs per device is demonstrated below: Lead / Slaves... Device1 -> Device2 -> Device3 -> Device4 -> Device5 -> Device6 Design1 Design2 Design4 Design7 Design10 Design12 Design3 Design5 Design8 Design11 Design6 Design9 To store all combinations of the above daisy-chains would result in the same designs being stored in multiple memory locations. Solution 1: This solution record assumes basic knowledge of FPGA configuration and file generation. Please consult the Development System Reference Guide for information on using the BITGEN and PROMGEN utilities. A daisy chain configuration stream can be realized as multiple separate files on a per device basis. However, some limitations apply. The configuration file for a lead device in the chain may not be used to program a slave device, and vice-versa. Procedure: 1. Create a bitstream (.bit) file for each design/device combination. The same bitstream may not be used for different device architectures. 2. Create an ASCII-HEX (.hex) file for each bitstream. 3. For all .hex files, except those intended for Lead Devices, remove the first 10 hex characters. These represent the 40-bit header of the configuration data. 4. Calculate the number of configuration bits remaining in each file. One way to accomplish this is: bits = (Bytes_per_file - number_of_lines) x 4 bits_per_character 5. Adjust file size to match the standard "Program Data" value in the Databook plus 8. Every file will have some padding at the end of the file in the form of `F's hex. Adding an `F' to the end of the file will increase it's size by 4 configuration bits. Removing an `F' will decrease the number of configuration bits by 4. All bit files intended for the same device must be equal in length. Lead device files should be 40 bits larger than slave device files because of the configuration data header. 6. Calculate the LengthCount for the Daisy-Chain. The LengthCount number is the total number of configuration bits for the chain of devices chosen minus seven: LengthCount = Total Configuration bits - 7 The total number of Configuration bits is the sum of configuration bits per device; where bits per device is Program Data + 8. 7. Replace original LengthCount value in all Lead configuration files with new value. The hex files will most likely be `byte-swapped'. The first 5 bytes must be unswapped to extract the old LengthCount number, replace it with the new one, and re-swap the bytes before inserting them into the file. For example: The original header may look like: FF043C89F9 Unswapping this would yield: FF203C919F The LengthCount is the 24-bit word succeeding the preamble `FF2', which in this case would be: 03C919. If our calculated lengthcount from step 6, was: 0F4099, then replacing the lengthcount and re-swapping would yield: FF20F4099F (Unswapped) FF042F90F9 (Swapped) This would replace the first five bytes in each of the Lead device configuration files. 8. Convert the hex files to the desired format for memory storage. The Xilinx web site contains a utility for converting hex files to prom files:   ftp://ftp.xilinx.com/pub/utilities/prom/pconfig.zip End of Record #3017 - Last Modified: 09/24/98 18:07

For the latest news, design tips, and patch information on the Xilinx design environment, check out the Technical Tips!