Blitter6502OISC_small.v:
- Added uart_sent flag to prevent UART retransmission
- Verified via Verilator: UART sends exactly one byte on halt
- Test byte: 0xAA (recognizable pattern)
research_stack_top.v:
- Auto-start logic (100ms after reset, no button needed)
- LED shows heartbeat when CPU running, register values on halt
research_stack_tangnano9k.cst:
- uart_tx=17, uart_rx=18 (matches Sparkle reference design)
Simulation results (Verilator):
- uart_test.v: 115 bytes in 300K cycles (continuous TX verified)
- research_stack_top: UART fires after Blitter halt, 0xAA byte sent
- LED pattern changes from IDLE to RUNNING to HALTED
