bhaskar1001101 / fromthetransistor

From the Transistor to the Web Browser, a 12 week journey

From the Transistor to the Web Browser

This is my attempt to understand the modern computer stack by implementing a toy version of it.

Inspired from geohot/fromthetransistor.

Section 1: Intro: Cheating our way past the transistor -- 0.5 weeks

• So about those transistors -- Course overview. Describe how FPGAs are buildable using transistors, and that ICs are just collections of transistors in a nice reliable package. Understand the LUTs and stuff. Talk briefly about the theory of transistors, but all projects must build on each other so we can’t build one.
• Emulation -- Building on real hardware limits the reach of this course. Using something like Verilator will allow anyone with a computer to play.

Section 2: Bringup: What language is hardware coded in? -- 0.5 weeks

• Blinking an LED(Verilog, 10) -- Your first little program! Getting the simulator working. Learning Verilog.
• Building a UART(Verilog, 100) -- An intro chapter to Verilog, copy a real UART, introducing the concept of MMIO, though the serial port may be semihosting. Serial test echo program and led control. Try out in Vitis/Vivado.

Section 3: Processor: What is a processor anyway? -- 3 weeks

• Coding an assembler(Python, 500) -- Straightforward and boring, write in python. Happens in parallel with the CPU building. Teaches you RISC-V assembly. Initially outputs just binary files, but changed when you write a linker.
• Building a RISCV CPU(Verilog, 1500) -- Break this into subchapters. A simple pipeline to start, decode, fetch, execute. How much BRAM do we have? We need at least 1MB, DDR would be hard I think, maybe an SRAM. Simulatable and synthesizable in Vitis/Vivado.
• Coding a bootrom(Assembler, 40) -- This allows code download into RAM over the serial port, and is baked into the FPGA image. Cute test programs run on this. Should be interesting.

Section 4: Compiler: A “high” level language -- 3 weeks

• Building a C compiler(Haskell, 2000) -- A bit more interesting, cover the basics of compiler design. Write in haskell. Write a parser. Break this into subchapters. Outputs RISC-V assembly.
• Building a linker(Python, 300) -- If you are clever, this should take a day. Output elf files. Use for testing with QEMU, semihosting.
• libc + malloc(C, 500) -- The gateway to more complicated programs. libc is only half here, things like memcpy and memset and printf, but no syscall wrappers.
• Building an ethernet controller(Verilog, 200) -- Talk to a real PHY, consider carefully MMIO design.
• Writing a bootloader(C, 300) -- Write ethernet program to boot kernel over UDP. First thing written in C. Maybe don’t redownload over serial each time and embed in FPGA image.

Section 5: Operating System: Software we take for granted -- 3 weeks

• Building an MMU(Verilog, 1000) -- RISC-V-ish, explain TLBs and other fun things. Maybe also a memory controller, depending on how the FPGA is, then add the init code to your bootloader.
• Building an operating system(C, 2500) -- UNIXish, only user space threads. (open, read, write, close), (fork, execve, wait, sleep, exit), (mmap, munmap, mprotect). Consider the debug interface you are using, ranging from printf to perhaps a gdbremote stub into kernel. Break into subchapters.
• Talking to an SD card(Verilog, 150) -- The last hardware you have to do. And a driver
• FAT(C, 300) -- A real filesystem, I think fat is the simplest
• init, shell, download, cat, ls, rm(C, 250) -- Your first user space programs.

Section 6: Browser: Coming online -- 1 week

• Building a TCP stack(C, 500) -- Probably coded in the kernel, integrate the ethernet driver into the kernel. Add support for networking syscalls to kernel. (send, recv, bind, connect)
• telnetd, the power of being multiprocess(C, 50) -- Written in C, user can connect multiple times with telnet. Really just a bind shell.
• Space saving dynamic linking(C, 300) -- Because we can, explain how dynamic linker is just a user space program. Changes to linker required.
• So about that web(C, 500+) -- A “nice” text based web browser, using ANSI and terminal niceness. Dynamically linked and nice, nice as you want.

Section 7: Physical: Running on real hardware -- 1 week

• Talking to an FPGA(C, 200) -- A little code for the USB MCU to bitbang JTAG.
• Building an FPGA board -- Board design, FPGA BGA reflow, FPGA flash, a 50mhz clock, a USB JTAG port and flasher(no special hardware, a little cypress usb mcu to do jtag), a few leds, a reset button, a serial port(USB-FTDI) also powering via USB, an sd card, expansion connector(ide cable?), and an ethernet port. Optional, expansion board, host USB port, NTSC TV out, an ISA port, and PS/2 connector on the board to taunt you. We provide a toaster oven and a multimeter thermometer to do reflow.
• Bringup -- Compiling and downloading the Verilog for the board