2 layers104.1 × 71.1 mm
Minifp
eigenco/frankenpi
This is an experimental project to connect Raspberry Pi with the help of cheap Cyclone IV FPGA board to 8-bit ISA bus to act as multiple different devices.
69 parts139
2 layers102.8 × 73.8 mm
This is an experimental project to connect Raspberry Pi with the help of cheap Cyclone IV FPGA board to 8-bit ISA bus to act as multiple different devices.
- Size
- 102.8 × 73.8 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 18
- Nets
- 101
- Pads
- 227
- Tracks, vias
- 543, 130
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 6 (file 20211014)
- Created
- 17 Jul 2022
- Updated
- 11 Nov 2023
Overview
CPU is an open-source printed circuit board by eigenco, from the eigenco/frankenpi repository on GitHub. It is a 2-layer board of 102.8 × 73.8 mm with 18 parts on 101 nets, routed with 543 tracks and 130 vias.
Its parts include 8 resistors, 7 connectors, 1 capacitor and 1 IC.
README
README.mdfrankenpi
This is an experimental project to connect Raspberry Pi with the help of cheap Cyclone IV FPGA board to 8-bit ISA bus to act as multiple different devices.
What is currently implemented (to some degree), i.e. PC can access through ISA
- Mass storage access from a file on the Raspberry Pi (written sectors are flushed every 2 seconds by default)
- Adlib output to optical SPDIF
- Sound Blaster 8-bit mono with DMA and IRQ (basic functions only), output to optical SPDIF
- Gravis Ultrasound (basic wavetable only), output to optical SPDIF
- Roland MT-32 (UART only), output to optical SPDIF
- USB mouse plugged into the Raspberry Pi will appear as a kind of serial mouse in DOS, custom ctmouse driver is provided (start with /v)
- Boot from custom TVGA9000i VGABIOS, i.e. no other devices are required to be present in the ISA bus besides FrakenPi and VGA-adapter
Youtube links:
https://www.youtube.com/watch?v=1ej76w8sHxY
https://www.youtube.com/watch?v=CkwgHHmKaSI
TESTED and working:
- Wolfenstein 3D (SB & Adlib)
- Second Reality (GUS)
- Scream Tracker 3.21 (SB1 and GUS)
- Skyroads (SB & Adlib)
- Keen 4 (Adlib)
- Monkey Island (Adlib/MT32/Mouse)
- Space Quest 3 (Adlib/Mouse)
- Space Quest 4 (Adlib/MT32/Mouse)
- Lotus 3 (Adlib)
- Lemmings (Adlib/Mouse)
- Eye of the Beholder I & II (Adlib/Mouse)
- Indiana Jones and the Fate of Atlantis (Adlib/MT32/Mouse)
Planned
- General MIDI
- MPU-401 support
- Sound Blaster AWE32 wavetable support
- Standard ATA at ports 1f0h-1f7h
- Compatibility improvements
- Boot ROM in the FPGA so hacked VGABIOS isn't required
- VGA output
Used resources
- Harddisk: ports 170h-171h
- SoundBlaster: ports 22ah-22eh corresponding ot base address of 220h, IRQ 7 and DMA 1
- MT32: 330h-331h
- Gravis Ultrasound: ports 341h-347h corresponding to base address of 240h
- Adlib: ports 388h-389h (standard)
- Mouse: port 3f8h and IRQ 4 (COM1)
- Bootcode for custom int 13h resides in hacked VGABIOS at the end of C0000-C7FFF memory region
Further explanation
- Outgoing port operations are transferred from the FPGA to the Raspberry Pi GPIO using dedicated unidirectional 8-bit data bus
- Incoming data from the Raspberry Pi GPIO (PCM, harddisk, mouse) is transferred using dedicated unidirectional 8-bit data bus
- Raspberry Pi: CPU0 handles hdd flushing and mouse, CPU1 handles GPIO transfers, CPU2 handles Adlib, Gravis Ultrasound and MT32 (software selected)
- Raspberry Pi operates with CPU1-CPU3 in isolated mode, all CPUs run at constant 1 GHz and sched_rt_runtime_us is -1
- Raspberry Pi generates sound data 64 samples at a time (16-bit stereo corresponds to 256 bytes it must transfer every 1.45ms or so)
- SPDIF is running in 24-bit 44100 Hz Stereo
- Hardcoded harddisk type is CHS 256/16/63, i.e. approx. 126MiB
Plan for the next PCB
- ICE40HX8K-CT256 (FPGA) seems to be available at Mouser
- IS61WV102416FBLL-10TLI (2 MByte SRAM) seem to be available at Mouser
- Created KiCAD project (PCB_v2)
Parts
18| Qty | Value | Footprint | References |
|---|---|---|---|
| 8 | 10k | Resistor_SMD:R_0603_1608Metric | R1, R2, R3, R4, R5, R6, R7, R8 |
| 4 | Conn_02x08_Odd_Even | Connector_PinHeader_2.54mm:PinHeader_2x08_P2.54mm_Vertical | J1, J2, J3, J66 |
| 1 | 0.1u | Capacitor_SMD:C_0603_1608Metric | C1 |
| 1 | 74LS688 | Package_DIP:DIP-20_W7.62mm_Socket | U19 |
| 1 | Bus_ISA_8bit | adlib:BUS_PC | J5 |
| 1 | Conn_02x09_Odd_Even | Connector_PinHeader_2.54mm:PinHeader_2x09_P2.54mm_Vertical | J4 |
| 1 | Raspberry_Pi_2_3 | Connector_PinHeader_2.54mm:PinHeader_2x20_P2.54mm_Vertical | J6 |
| 1 | TOTX1350_F_ | SamacSys_Parts:TOTX1350F | CS1 |
Questions
How big is the CPU PCB?
It measures 102.8 × 73.8 mm and has 2 copper layers, 1.6 mm thick.
What parts does the CPU use?
18 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the CPU KiCad files?
From the eigenco/frankenpi repository on GitHub, at the commit this page was made from: the board is KiCad/CPU.kicad_pcb and its schematic KiCad/CPU.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the CPU design in my own project?
Its repository states no licence, so its author keeps all rights: ask eigenco before reusing the design.
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