[039] Multi-Cycle Microcode! - Building a CPU From Scratch

Опубликовано: 23 Февраль 2025
на канале: rj45 Creates

2,120

To load and store from slow memory, we need to be able to wait for that memory to finish. To do this, let's implement a microcode sequencer and the ability to loop until memory is finished! This implements memory request and acknowledge.

This is in a CPU built from scratch using Digital, a digital logic simulator we can use to build a CPU that can run on an FPGA.

See the project on github here: https://github.com/rj45/rj32
Get the program I am using here: https://github.com/hneemann/Digital/r...
Get the assembler I am using here: https://github.com/hlorenzi/customasm

If you would like to support this work and encourage me to make more videos:
https://ko-fi.com/rj45_creates

00:00 - Intro
01:10 - Possibilities
02:30 - Microsequencer Circuit
03:18 - Step Register
04:47 - Microcode Memory Layout
06:25 - Op or Step
08:58 - Microsequencer Integration
09:33 - Microcode Updates
14:14 - Wiring the Next Field
15:21 - Testing Halt/Error
15:54 - Stall and Fetch Explanation
17:30 - Inhibiting Fetch
20:24 - Testing Fetch Inhibition
21:00 - Inhibiting Stall
22:11 - Testing Stall Inhibition
22:28 - Fixing Skip With Enable
25:19 - Testing Skip
25:43 - Deciding With Flags
30:05 - Microcode For Decisions
34:35 - Memory Req and Ack
37:09 - Testing Req and Ack
38:07 - Summary

Digital Logic Introduction:
Exploring How Computers Work -    • Exploring How Computers Work
How Do Computers Remember? -    • How Do Computers Remember?

Deeper dive into how to build a computer from scratch:
Ben Eater's 8-bit Breadboard Computer -    • 8-bit computer update