Emulation
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30 May 2021
Breaking and fixing the RISC-V Store-Conditional instructions
Trying to debug the Linux boot process on the emuriscv RISC-V emulator has led me to discover another fun bug, one that appears when you don’t read the specification as thoroughly as you should. The …22 Apr 2021
(Mis)understanding RISC-V ecalls and syscalls
After spending some time with emuriscv and attempting to boot Linux into a shell I realized that I’m doing something really wrong regarding system calls. RISC-V offers an ecall (Environment Call) …18 Apr 2021
Online RISC-V disassembler
Making a nicer disassembler I’ve had a rudimentary disassembler in the emuriscv emulator, but compared to other disassemblers out there it was not very refined. Debugging and fixing the emulator …04 Apr 2021
RISC-V supervisor mode
RISC-V features multiple privilege levels (machine, hypervisor, supervisor and user mode). The cores (harts) power up in machine mode, which is mandatory in all RISC-V implementations. Operating …03 Apr 2021
Booting RISC-V on QEMU
For reference, I wanted to check how qemu boots RISC-V Linux. Loosely following a guide , I describe how to build and boot a Linux environment targeting the 32-bit RISC-V architecture. There are three …Revisiting RISC-V emulator in 2021
This week I’ve revisited my RISC-V emulator project emuriscv - https://github.com/jborza/emuriscv , as I’m still intrigued by the idea of booting Linux on my own CPU emulator. I’ve worked on and off …04 Feb 2021
CHIP-8 on Nokia 3410
Mobile development like it’s 2002 I thought it’d be fun to develop something for a mobile phone. Thus I did a quick port of my previous CHIP-8 emulator from C to Java. Nokia 3410 looked like a fun …23 Dec 2020
CHIP-8 emulators inconsistent behavior
CHIP-8 arithmetic behavior and VF variable I’ve been fiddling with CHIP-8 and writing a sample program in Octo - a CHIP-8 IDE/assembler with a nicer scripting language than raw opcodes. I wanted to …2 min read - chip807 Dec 2020
CHIP-8 emulator in C
CHIP-8 is one of the most popular target architectures for aspiring emulator writers. I’m planning to implement it in hardware, so I thought that writing a software emulator/interpreter would be …05 Sep 2020
MCPU emulator (and ATTiny85 port)
MCPU is a neat minimal 8-bit CPU (CPU design by Tim Boescke in 2001, cpldcpu@opencores.org ) - see its opencores project file and GitHub repo . It fits into 32 macrocells on a CPLD and can operate on …19 Apr 2020
Writing a monitor console for emuriscv
As a follow up to the previous post Debugging things running in your emulator I thought it would be nice to write a monitor console for the emuriscv RISC-V emulator. With a monitor console one can …16 Apr 2020
Updating the RISC-V Linux environment
As I planned to work some more on the emuriscv RISC-V emulator, I wanted to upgrade from Linux 4.15 and buildroot from 2018 to something more recent. Buildroot-2020-02 supports compiling the image …12 Apr 2020
Test-driven emulator development
Test-driven development is a software development process where you write a test before writing a code that satisfies that test, then refactor and continuously validate that the requirements are still …11 Apr 2020
Debugging things running in your emulator
You’ve written an emulator, how do you debug anything running inside? In this post I’ll try to describe what I did (and thought of doing), starting from the most crude methods. Using the IDE and debug …09 Apr 2020
Building up a RISC-V Linux with Buildroot
A friend told me about a cool new open-source instruction set architecture called RISC-V (pronounced risk-five). As I wanted to learn more about the architecture, I decided writing an RISC-V emulator …20 Oct 2019
Fantasy console on a console
Back in April 2019 I decided to get into emulation and thought about writing a simple one. I read about the MOS 6502 microprocessor and it looked promising as it was used in famous products such as …