Building the site
The Astro site for 6502.dbhq.uk is built one task at a time, starting with a registry of machines that a test keeps in step with the family document.
Built in public
A 6502, built in the open
A cycle-accurate 6502 and 65C02 core in C#, and the machines it will run, as many as possible, each one proven. Every step of the work is written down here, as it happens.
Status
Where it stands
Every figure on this page comes from the latest test run, whose commit is shown below, or from a dated measurement. None is typed by hand.
0 of 51
Machines implemented
A machine counts only once it runs in the browser and passes an automated test.
5
Variants of the core
The NMOS 6502, the NES's 2A03, and three 65C02s.
1,480
Tests passing
From the latest test run, on the commit shown below.
24.4 times
Against a 2 MHz machine, in the browser
Compiled ahead of time, best of 5 runs, on one machine, collected 30 Sept 2026. The design target is at least 25 times real speed, for the core alone. Against this site's 2 MHz reference it is met natively and not yet met in the browser.
Test run on commit 1393d10.
Proof
A difference is a number, not an argument
The core is checked against Tom Harte's SingleStepTests, a published record of every opcode's bus activity, cycle by cycle. When something differs, the test names the cycle and the byte.
Where it knowingly differs from a reference, that is written down too.
Passed Nmos6502Harte: 256 Passed Ricoh2A03Harte: 256 Passed Rockwell65C02Harte: 256 Passed Synertek65C02Harte: 256 Passed Wdc65C02Harte: 254 Passed! - Failed: 0, Passed: 1,480, Skipped: 0
Machines
The machines this core is for
The first three, and the whole family in the table.
Planned
KIM-1
1976, 6502, 1 MHz
Planned
BBC Micro
1981, 6502, 2 MHz
Planned
NES, Famicom
1983, Ricoh 2A03 (NTSC), 2A07 (PAL)
Journal
From the journal
What was decided, what was checked, what went wrong and why.
The programme changes shape
The site's look, its imagery, and a mission that grew from three machines to as many as possible.
The browser speed check
How fast the core runs in a browser, interpreted and compiled ahead of time, measured on one machine.
Illustration: the textured backgrounds behind the proof and machines sections are generated, not measurements