Turbo V

The Turbo V is a (for now) hypothetical bare-metal retro-inspired computer which runs a RISCV soft-core on an ICE40 FPGA. It borrows some fundamental design ideas from the Commander X16 but with some changes to fit the FPGA architecture and 32-bit platform, along with necessary modern constraints due to availability of through hole chips.

This is just a fun thought exercise for now. Assuming the hardware actually can work, there is no kernel.

Contents:

• Tower of Power
• System Bus
• Memory Map
• System MCU
• Cards
  • Basic RAM
  • Smart RAM
  • VERA
  • TurboWave
• Kernel

Loose High Level Specs

• CPU: FPGA-based RV32IMC RISC-V core (PicoRV32 on iCE40 UP5K) at ~48 MHz
• 128 KB zero-wait FPGA SPRAM (internal system RAM)
• 256 B internal FPGA boot ROM (reset vector -> jump to system ROM)
• 512 KB motherboard flash ROM (flat mapped, A0-A18 direct)
• Expansion Bus:
  • 12 MHz
  • 19-bit address / 8-bit data
  • 512 KB per-device window optionally split into control/data segments
  • 8-bit bank latch in control window -> 64 MB addressable per device
  • Per device bus divisors
  • 8 device selects via 74HC138 (3-to-8) - 6 expansion slots + ROM + system controller
  • Single shared IRQ (nIRQ), active-low open-drain
  • Interrupts: PicoRV32 custom mechanism (PC saved to q0, return via retirq)
  • Per-slot dedicated stereo returns (mixed on the motherboard)
  • -/+ 12V and 3.3V rails
  • Repurposed PCIe connectors
• I/O MCU (RP2350, PGA2350)
  • USB keyboard/mouse
  • SNES controllers
  • SD card storage
  • Timers
  • User Flash Storage (Boot Options, etc.)
• Video/Audio: VERA on expansion card (primary video + PSG/PCM audio)
• Audio: TurboWave on expansion card (optional)

Contributions and Clarity

I want to be clear what tools and resources I used to help ratify the design. I have had the basic design in my head for quite a while but it had gaps that needed clarification. This includes the use of AI tools to help with brainstorming, part finding, searching, etc. Specifically I used Kagi's AI assistant (specific Kimi K2.6) to brainstorm. I did not use AI to write any code or any of this documentation.