#469 – An Interview with Craig J Bishop

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Welcome, Craig J Bishop!

• Craig designed and built the Gameslab, which is a custom gaming platform built with a Xilinx Zynq part (XC7Z035). (Update: Craig has been posting more about the Gameslab on his site here)
• Bought reballed chips on PCBs. They were actually a $1200 chip he got for $80.
• Episode with Ryan Cousins
• There is apparently a kit for counterfeiting Xilinx chips
• National lab has a pdf on how to detect counterfeits
• Digilent Zybo
• Craig built the board on the JLC 6 layer process at 210×100 for each board. $150 for 5 PCBs.
• DDR3 chip was .8mm pitch
• Using stack up to calculate impedance/prop delay
• Used an excel sheet to track delay and skew for nets, since KiCad can’t track delays between layers
• FPGA on chip delays are also stated in the datasheet and need to be accounted for.
• Running Rust on STM32L0, on kernel modules in A9, applications / games
• Sense resistors with instrumentation amps going to the ADC to measure each rail’s current draw.
• BQ24250 chip for charging with configurable registers
• Zynq doesn’t necessarily need the bitstream programmed first. Instead the A9s boot first and can load the bitstream.
• Every game brings its own hardware
• Can put the Gameboy hardware into the fabric!
• Craig doesn’t like verilog, so he uses a higher level language called SpinalHDL. It is a fork of Chisel, which is based on Scala.
• Each of the above languages are strongly typed. Loosely typed means you can convert between data types, like in C.
• “Verilog is becoming the assembly language of FPGAs”
• ZipCPU
• AXI bus
• Most designs need to reimplement different hardware blocks. But there are libraries in Chisel, which can implement things easier.
• Vex Risc V
• Created a frame buffer for the LCD and some 2d graphics acceleration on the Gameslab.
• Learned to program to make PC games. This was part of the idea behind the Gamesphere project as well.
• PIC18F452 in a 40 pin DIP
• Used AT91R4000 for the game sphere
• Andrei LaMothe wrote the book “The Black Art of video game console design”
• Cypress dual port SRAM
• Craig’s first “big boy job” was working for a a neighbor up the street starting a semiconductor packaging company (Tim Olson)
• Deca Technologies was opening a Wafer Level Chip Scale packaging fab in the Philippines.
• After iphone came out, there was a lot of demand for low profile complex chips.
• Raspberry Pi photon problem
• Added a “squishy” layer to the silicon, and then exposing certain parts of the silicon to the interconnect.
• The graphics problem was that they wanted to make the chip bigger but the silicon smaller
• EWLB from Infineon looks like a plastic wafer.
• Can put two chips next to each other
• There was a paper about the subject (has the image Chris and Craig were discussing during recording).
• Sometimes the parts are placed 30 microns to the left, which is not good for the substrate they are placed upon.
• Can get really expensive PnP machines but they go slow.
• The microscope would spit out X, Y and rotation, but it scales with chip complexity, such as when there are two chips.
• Needed to do traces between them
• Craig’s job was to take the output and do some autorouting between them.
• Feature sizes were 1 micron
• Package design looks like PCB design
• Cadence sells System in Package designer but is really Allegro with different plugins.
• Can people do their own SIP?
• Craig thinks that design will move towards more SIP
• Split die architecture
• Split it into a few pieces: This will help improve yield and flexibility, as well as modularity.
• Chris asked about Chiplets, a topic that is championed by Dr Subu (sp?)
• Chiplets are going to do interconnect in silicon, not plastic
• Example is BLE and micro
• Adaptive alignment
• Craig gave a talk at KiCon about how Autorouters work and how they have been improving.
• Not your grandpa’s autorouter
• Freerouting is nice and available but it’s not the latest
• TopoR
• Moving towards interactive design (P&R), but Craig thinks it should go the other way.
• Generative design would be better
• Dave Vandenbout’s SKiDL talk
• Craig was briefly interviewed by Piotr and Alvaro at KiCon
• Find Craig on his personal site where he is documenting his projects (craigjb.com) and also find him as @craig_jbishop on Twitter.
• Check out the Phoenix 3H (hardware happy hour) if you’re in the area!