Carrier

Matt Venn's ASIC VGA Clock

• World's first certified open source hardware down to the GDS?
• The ASIC was part of the Google sponsored MPW1
• The ASIC is still in fabrication by Skywater, we expect silicon in September 2021.
• For more details about the implementation, see VGA ASIC Clock.
• RTL: https://github.com/mattvenn/vga-clock
• Application details: https://efabless.com/projects/14

PCB

This PCB provides all the necessary components to make a functional clock:

• Pads for mounting the ASIC
• Decoupling
• Voltage regulators for core (1.8) and IO (3.3)
• Crystal oscillator
• SOIC-8 footprint for dual SPI flash for the configuration firmware
• 2x6 1.27mm header with housekeeping SPI, UART and 5V - the minimum connection needed for power and debug
• PDF Schematic

Setup

Firmware

Needs to active project 2. See https://github.com/mattvenn/caravel-mph/blob/release/verilog/dv/caravel/user_proj_example/vga-clock/vga_clock.c for the simulation test. Will need PLL setup to work on the ASIC.

Flashing

For flashing, see https://github.com/efabless/ravenna/blob/master/firmware/blink/Makefile as a starting point. ravenna_hkspi.py may need some tweaks to work with Caravel.

The SPI interface can be used to put the ASIC into 'passthrough' mode. Then the FLASH can be programmed through this same SPI interface.

See the schematic for the pinout of the SPI interface on the board.

PLL config

Needs 31.5MHz for VGA signal. As precise as possible for good timekeeping. Input oscillator is 9MHz.

Using https://github.com/kbeckmann/caravel-pll-calculator

matt-desktop:2003 [main]: ./caravel_pll.py generate --clkout 31.5 --clkin 9
PLL Parameters:

clkin:    9.00 MHz
clkout:   31.50 MHz
clkout90: 31.50 MHz

PLL Feedback Divider: 14
PLL Output Divider 1: 4
PLL Output Divider 2: 4

Register 0x11: 0x24
Register 0x12: 0x0e

Pinning

See the instantiation into the user project area here: https://github.com/mattvenn/multi-project-harness/blob/separate-macro/user_project_wrapper.v#L190 See the design repository here: https://github.com/mattvenn/vga-clock/tree/db029c38607c8d27f54b48bd8fd423cae3c4ed3d

vga_clock proj_2 (
    .clk(proj2_clk),
    .reset_n(proj2_reset),
    .adj_hrs(proj2_io_in[8]),
    .adj_min(proj2_io_in[9]),
    .adj_sec(proj2_io_in[10]),
    .hsync(proj2_io_out[11]),
    .vsync(proj2_io_out[12]),
    .rrggbb(proj2_io_out[18:13])
    );

• rrggbb is mapped to R1, R2, G1, G2, B1, B2
• 500R used for R1, G1, B1
• 1k used for R2, G2, B2

Power

User project

• Power is provided to the clock design only by VCCD1 and VSSD1.
• Tim Edwards suggests:
  • keeping VCCD2 and VCCD1, VSSD2 and VSSD1 tied together just to make sure there are no floating power supplies.
  • connect VDDA1 and VDDA2 to VDDIO, and VSSA1 and VSSA2 to VSSIO to make sure they're not floating.
    For reference, the power ring around the user project area has 4 buses. From outside to inside: VSSA2, VDDA2, VSSA1, VDDA1, VSSD2, VCCD2, VSSD1, VCCD1.
  • VSSA2 user area 2 ground
  • VDDA2 3.3V user area 2 psu
  • VSSA1 user area 1 ground
  • VDDA1 3.3V user area 1 psu
  • VSSD2 user area 2 digital ground
  • VCCD2 1.8V user area 2 digital psu
  • VSSD1 user area 1 digital ground
  • VCCD1 1.8V user area 1 digital psu

Management

• VDDIO/VSSIO power and ground for IO (up to 5v). I'm connecting to 3.3v
• VDDA/VSSA 3.3v PSU for management area
• VCCD/VSSD 1.8v PSU for management area

BOM

All available from digikey as of 13/7/21

• regulators
  • 1.8v MCP1824T-1802E/OT
  • 3.3v MIC5504-3.3YM5-TR
• flash: W25Q32JVSSIQ-TR
• oscillator: SIT8008AI-23-33S-9.000000
• VGA connector: L77HDE15SD1CH4F
• USB connector: 1050170001
• buttons: PTS636 SM25J SMTR LFS

Errata

v0.1

• Initial footprint for ASIC was flipped.
• All other components were tested and worked as expected.

v0.2

• TBD

Resources

• PCB forked from https://github.com/samlittlewood/caravel_carrier
• Caravel datasheet: https://caravel-harness.readthedocs.io/en/latest
• Logo created at: http://oshwmark.capablerobot.com/
• PCBs sponsored by https://OSHPark.com

License

• The PCB is licensed under the MIT License
• The ASIC is licensed under the Apache2 License
• The documentation is licensed under the CC0 License

Open Source Hardware

This board is an OSHWA approved design: ES000023