Ikos Pegasus reverse engineering
(→FPGA JTAG chain topology)
(→Connection of the FPGA JTAG chain to the CPLD)
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Revision as of 20:15, 11 August 2010
- The rack with the power supply can hold up to 7 boards connected via a backplane.
- One main board with:
- SCSI controller
- 5 auxiliary boards with (each):
- 1 XC95216 CPLD
- 64 XC4036XL FPGAs
- lots of SRAM
- One auxiliary board was destructively reverse engineered, so only 4 are remaining.
Some device photos are here.
Programming the auxiliary boards
In normal operation, the CPLD receives configuration data from the backplane (originating from the mainboard through the SCSI port) and distributes it to the FPGAs. The CPLD uses JTAG to send data to the FPGAs. The 64 FPGAs on each auxiliary board are arranged to form one big JTAG chain driven by the CPLD.
Because this mode of operation uses a proprietary protocol which is especially hard to reverse engineer since we do not have the original software and SCSI device driver, we are trying to program the boards with a JTAG probe.
The CPLD's JTAG port is accessible on each board with a HE10 connector following the MultiLINX pinout.
Legend: X = missing pin (key), NC = No Connect
We can use urJTAG to access the CPLD, with the BSDL files released by Xilinx to enable boundary scan. For an unknown reason, the Xilinx iMPACT tool fails to recognize the CPLD.
FPGA JTAG chain topology
All the 64 FPGAs are arranged in a daisy chain for TDI and TDO.
For TCK and TMS, the board is divided into 4 quadrants and these signals are shared within each quadrant.
Connection of the FPGA JTAG chain to the CPLD