New project board for TinyFPGA B2 boards (wip)


#1

I’m working on a project board for the TinyFPGA B2 boards. The general idea is for it to be used to implement existing retro computers or computers of your own design. This is a project board that you would assemble yourself.
To make it a bit easier all of the components are through-hole parts. It adds the following features to a TinyFPGA B2 board:

  • 128 or 64 Kilobytes SPI SRAM
  • MicroSD Card Slot in SPI mode
  • VGA output, 2-bits per color
  • PS/2 connector for a keyboard
  • USB-A host connector
  • Audio output jack
  • Prototyping area
  • Pico-ITX form-factor

The current work-in-progress design is looking like this:

EDIT: Updated image and SPI SRAM


#2

Here is something I don’t quite understand. I thought that to generate VGA signal FPGA needs at least 25 Mhz clock. However TinyFPGA B2 has only 16 Mhz clock. Will it work?


#3

Even though the on-board clock is 16MHz, the FPGA itself has a PLL. PLLs are able to take an input clock and multiply and divide the frequency to generate a large range of output frequencies, including 25MHz for VGA.

That being said, I have been considering a design of this board that works with either an A-Series or B-Series TinyFPGA. In that case I would include a 25.175 MHz crystal.


#4

Luke, more RAM please! I was just looking at the B2 to implement a homebrew 16- or 32-bit CPU, and bring up an OS like RetroBSD or xv6 on it. So something like 512Kb or 1Mb would be wonderful!

Thanks, Warren


#5

256KB is the most I can get with SPI SRAM. I think you would be much happier with the e-series when it comes out: http://hackaday.io/project/28266-tinyfpga-e-series


#6

Thanks for the reply Luke. I’m not sure if the ECP5 FPGA is supported by IceStorm. If not, I can buy a B2 and breadboard up a Microchip 1Mbit SRAM (or several), an SDHC socket and a UM245R UART. Cheers, Warren


#7

Ohh…I just found this: https://toptechbuy.com/products/microchip-23lc1024-i-sn-sram-ic-1mbit-sdi-sqi-20mhz-8-soic-1-piece

I’ll see if I can modify the SPI SRAM footprint to also accept the surface mount packages.


#8

@DoctorWkt actually, that part is also 1mbit. Hmm, you could use the breadboard area to add more SPI SRAM. You could easily get a total of 256KB and maybe 512KB if you are creative.


#9

You know, I think I just misread your post…bits vs bytes. Yes, I can sell it with 128 kilobytes, which would be 1 megabit. So I think it will have what you’re looking for :sweat_smile:


#10

That would be excellent Luke, and help support legacy system implementations with more than 64KB of RAM. I’ve just ordered my B2 :slightly_smiling_face:

Cheers, Warren


#11

The prototype boards arrived! Parts arrive today as well. I’ll build one up and test it out.


#12

Done soldering except for the audio low-pass filters. Need to figure out some reasonable R and C values. Was fun to solder! The production boards will have gold finishing (ENIG) vs tin (HASL).


#13

The TinyFPGA Computer Project Board is now available on Tindie! It will show you the full kit price including a discounted TinyFPGA B2 module. If you don’t want the module, there is an option to remove it. If you just want the bare board you can do that as well.


#14

Luke, will the e-series be compatible with icestorm by any chance?


#15

There’s not currently support for the ECP5 FPGA in the e-series. But I will be working to get support for it.


#16

Luke,

Received my TinyFPGA Computer Project Board kit today, only a few days after ordering on Tindie. Looks good. I wonder if you might be able to provide a PDF of the board schematic to help in assembling the kit?
And also wonder if there is a beginning design file to load into the B2 board to test out initial operation?

Thanks!