Can I store a userdata at the beginning of the BPI/SPI configuration memory?
Can I start configuration at addresses other than 0x000?
In Spartan-6 FPGA, the default Master configuration address is 0x000000, which is the beginning of the configuration memory for Master SPI/BPI/SelectMAP configuration mode.
In Spartan-6 you can store a userdata in configuration memory before the configuration memory start address (at the location 0x00000) in BPI or SelectMAP configuration mode only.
In Master SPI/Serial configuration mode, storing user-data before configuration memory should be avoided.
If it is used then it should not exceed 512 clock cycle.
This is because the Spartan-6 FPGA has a Master SPI Vendor Auto-Detection and Error Handling state machine, which runs at the power cycle or at the PROG_B/JPROG signals.
If the Synchronization word does not detected before 512 cycles then FPGA configuration will fail with INIT_B LOW.
As a result you should take precautions when storing user-data prior to the configuration memory in configuration flash memory.
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