FPGA / MCU 'Open Source' project - Page 1
Forum section: electronics / projects

author: CM800
author_rank: Frequent Contributor
timestamp: August 01, 2018, 10:47:11 am
content: Hi All,I'm looking to design a little FPGA / MCU combo board. I wanted to get some input from the community on a few thoughts:The FPGA of choice is the ICE40UP5K-SG48, the same unit as the UPDuino, it also supports icestorm which is a major bonus.I would like some input as to what MCU would be most useful to everyone. I'm imaging maybe a Cortex M3 such as the STM32F103C8. A relitively common unit that supports stm32duino as well (added bonus)Feedback I would like:- What MCU would people prefer?- SD card holder yes/no? (could this be used to even update the MCU / FPGA possibly?)- 2.54mm pitch connections? or go for a card edge or base connector with a breakout for 2.54mm? (maybe both options?)- FT series USB-Serial / programmer cable? (Maybe the FT4232? Port A: MCU Programming, Port B: FPGA Programming, Port C/D going to FPGA or MCU as application comms?- Any other thoughts?

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 01, 2018, 05:42:19 pm
content: Since the ICE40UP5K is a low power FPGA, I would tend to favor a low power uC to complement it. If you're going for an STM32, I'd go for the L4 line (cortex M4 low power series).As for the FTDI chip, if you're going for a multi-channel one, just make sure that one channel can be used as SPI and will be compatible with the programming tools. AFAIK, the iCE40UP series uses an SPI port for programming and not a more standard JTAG port.Speaking of programming, I think it could be interesting (maybe with a couple jumpers) to route an SPI port from the uC to the FPGA, thus allowing the uC to program it on the fly. Could be a nice addition IMO.

author: CM800
author_rank: Frequent Contributor
timestamp: August 01, 2018, 06:26:35 pm
content: Quote from: SiliconWizard on August 01, 2018, 05:42:19 pmSome good points / thoughts there. I've never thought about low power... ever. I guess some people might have interest in that kind of thing. Should be considered indeed.Nice idea for passing it through. It's something I considered, it could pull bitstreams from a SD card, that way you could have thousands of peripherals stored in it, and it could change them on the fly... nice.Is it thought that a low end FPGA / MCU combo would be nice, or should it be upscaled more towards.. say, an M7 processor or even an A9, or something linuxable.I hold a slight reservation for that, as really it becomes someone else's project as it's beyond my comfort level I feel. No experience with high speed design.

author: iMo
author_rank: Super Contributor
timestamp: August 01, 2018, 06:41:27 pm
content: QuoteUpduino @30MHz 20mA (half full), stm32f103c8 @72MHz the same.You may subtract 3-6mA from both (voltage regulators, etc.)..ice40UP5k has got 2x hardware SPI, 2x hardware I2C, plus the special SPI for programming could be used off the userland as well (you may store your user data into the bitstream flash off your fpga design, for example). The only issue you will encounter soon or later is the number of IO pins available.. A 64pin version would be nice to have..