micheleandClaude Sonnet 5
a4c080da83
Implements the user's board architecture: config flash wired exclusively to the FPGA, host (ESP32) reaches it only through the FPGA. flash_spi_master.v is a plain byte-wide SPI master using STARTUPE2 to reclaim CCLK after configuration (the real, Xilinx- documented "indirect SPI flash programming" technique, UG470 p94-96). New opcode 0x40 FLASH_XFER in spi_host_bridge_v3.v relays bytes byte-for-byte between host and the physical flash bus -- the host decides the exact SPI NOR command sequence (verified against the real W25Q32JV datasheet), this RTL knows nothing about flash semantics. Found and fixed two real bugs during verification: a byte-assembly off-by-one in flash_spi_master.v, and a genuine protocol-latency bug in the FLASH_XFER opcode's response timing (needed 2 trailing margin bytes, not 1 -- the internal flash transfer doesn't start until the triggering byte finishes, so 1 byte of margin isn't enough). 39/39 tests pass end to end (host SPI -> bridge -> flash_spi_master -> behavioral flash model). Wired into n2_system_ddr3_top.v with real pin constraints (flash_mosi =K17/flash_miso=K18/flash_cs_n=L13, the same pins reserved-but-unused in EXP-0075) and BITSTREAM.CONFIG.PERSIST=FALSE made explicit. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MUG92aM9m68TRc4rG55BcC