Computers are made up of a collection of switches (or transistors) which circuit designers then combine to create basic logic gates (AND, OR, XOR, NOT, NAND, etc.), which are then built in to more complex computing modules (such as Adders, Arithmetic Logic Units (ALUs), or Floating Point Units (FPUs)). These modules are then combined into an overarching computer architecture which is exposed to applciations and/or programmersr for manipulating different computational tasks. For example, below is the ARM6 core architecture which is used in the SAMD11 microchip: \
<imgsrc="./imgs/arm6_core.png"height="500">\
Computers are made up of a collection of transistors which circuit designers combine to create basic
logic gates (AND, OR, XOR, NOT, NAND, etc.), which are then built in to more complex computing
modules (such as Adders, Arithmetic Logic Units (ALUs), or Floating Point Units (FPUs)). These
modules are finally combined into an overarching computer architecture which is exposed to
applications/programmers. For example, below is the ARM6 core architecture which is used in the
When programming a SAMD11, you can control what information is written and read from the registers along with which instructions are passed to the control unit by changing the software flashed on the processors memory; however, you have no control over the underlying hardware.
When programming a microcontroller like the SAMD11, you can control what instructions are passed to
the control unit (and thus what information is written and read from memory/registers) by changing
the software flashed on the processor's memory; however, you have no control over the underlying
hardware.
FPGA stands for **"Field Programmable Gate Array"** - it is a collection of integrated circuit logic
gates and interconnects which can be programmed and reconfigured directly by the developer. This is
very different from any other type of computer or microcontroller because you now have control over
the hardware and can define custom circuits.
FPGA stands for **"Field Programmable Gate Array"** - it is a collection of integrated circuit logic gates and interconnects which can be programmed and reconfigured directly by the developer. This is very different from any other type of computer or microcontroller because you now have control over the hardware and can define custom circuits of a prepackaged chip. \
[intro to FPGA architecture](https://towardsdatascience.com/introduction-to-fpga-and-its-architecture-20a62c14421c)
## programming FPGAs (Verilog)
To program an FPGA, you use a hardware description langauge, here we'll focus on [Verilog](https://www.verilog.com/), but [VHDL](https://en.wikipedia.org/wiki/VHDL) is also commonly used and simiar. Hardware Description langauges can be thought of as a markup langauge for circuit layout - basically you're only one abstraction layer above defining gate level logic. This changes the philosphy for writing algorithms and applications in meaningful ways, most noteably:
- all statements are executed concurrently. unlike a simple C program that will be executed line by line inside the main() block, each line in verilog (except those between begin and end statements) are executed at the same time.
- verilog code is synthesized and then everything is mapped to hardware gates; as opposed to other langauges which are compiled and stored somewhere that the CPU may or may not access.
Put simply, verilog code is built up of modules, which have defined inputs and outputs (they can be thought to bee similar to functions), which execute combinatorial logic and/or pass values between registers. For example, a full 1-bit adder in verilog looks like this
To program an FPGA, you use a hardware description langauge, here we'll focus on
[Verilog](https://www.verilog.com/), but [VHDL](https://en.wikipedia.org/wiki/VHDL) is also commonly
used and simiar. Hardware Description langauges can be thought of as a markup langauge for circuit
layout - basically you're only one abstraction layer above defining gate level logic. Keep in mind
that unlike programming languages they don't define sequences of instructions - they define
schematics. This changes the philosphy for writing algorithms and applications in meaningful ways,
most noteably:
- All statements are executed concurrently. Unlike a simple C program that will be executed line by
line inside the main() block, each line in verilog (except those between begin and end statements)
is executed at the same time.
- Verilog code is synthesized and then everything is mapped to hardware gates; as opposed to other
langauges which are compiled and stored somewhere that the CPU may or may not access.
Verilog code is built up of modules, which have defined inputs and outputs (they can be thought to
bee similar to functions), which execute combinatorial logic and/or pass values between registers.
For example, a full 1-bit adder in verilog looks like this
```
module full_adder(
input in_bit_1,
...
...
@@ -37,20 +68,34 @@ module full_adder(
assign o_carry = w_WIRE_2 | w_WIRE_3;
endmodule
```
which is just a written implementation of a full adder logic circuit \
which is just a written implementation of a full adder logic circuit.
<imgsrc="./imgs/full_adder.png"height="500">
## programming toolchain
Unlike programming a microcontroller (code is _compiled_ --> a binary file is generated -> then that binary data is stored into the flash memory of the chip), verilog needs to be _synthesized_:
1. The synthesis tool expands the verilog code into a gate level netlist following rules given by some predefined library. [Yosys](http://www.clifford.at/yosys/) is a commonly used open-source RTL synthesis tool for this
2. Then the netlist is passed to a "place and route" (pnr) tool which grounds the netlist in the physcial world by figuring out the placement and routing between logic gates. [nextpnr](https://github.com/YosysHQ/nextpnr) pairs well with yosys for this.
3. Finally, the output of the pnr tool is passed to the FPGA hardware as a bistream and the physical hardware is modified.
## stopwatch hello-world
The iCEBreaker FPGA breakout board is a great platform for hello-worlds beginner FPGA development. Refer to the [icebreaker-fpga-workshop](https://github.com/icebreaker-fpga/icebreaker-workshop) for step by step instructions on installing the necessary tools and building a FPGA stopwatch.
The iCEBreaker FPGA breakout board is a great platform for hello-worlds beginner FPGA development.
Refer to the [icebreaker-fpga-workshop](https://github.com/icebreaker-fpga/icebreaker-workshop) for
step by step instructions on installing the necessary tools and building a FPGA stopwatch.
## why??
FPGAs have been growing in popularity, especially among hobbyists and academics, over the last 5 - 10 years as open source development tools have become more accessible and custom hardware optimizations become more important for ultra-low power embedded applications. FPGA programming has a wide range of applications
FPGAs have been growing in popularity, especially among hobbyists and academics, over the last 5 -
10 years as open source development tools have become more accessible and custom hardware
optimizations become more important for ultra-low power embedded applications. FPGA programming has
a wide range of applications
- accelerated machine learning algorithms
- image / video processing
- high speed data acquisition at the edge (e.g. particle accelerators)
...
...
@@ -58,5 +103,3 @@ FPGAs have been growing in popularity, especially among hobbyists and academics,
- ASIC / architecture prototyping
-[opencores](https://opencores.org/)
- basically anything with vertical development (limited in quantity with highly specialzed task)
