15.2.7 Worked Examples: Beta Junkyard | Summary and Q&A

395 views
July 12, 2019
by
MIT OpenCourseWare
YouTube video player
15.2.7 Worked Examples: Beta Junkyard

TL;DR

This analysis explores the behavior of four categories of discarded 5-stage pipelined Betas and how they execute a given test program.

Install to Summarize YouTube Videos and Get Transcripts

Questions & Answers

Q: How does the test program help determine the category of the discarded Betas?

By single-stepping through the program and noting the address loaded by the final JMP instruction, we can identify the category based on the observed behavior and differences compared to a fully functional Beta.

Q: What is the purpose of bypass paths in the Betas?

Bypass paths allow instructions to directly access the correct values from other pipeline stages, bypassing the need to read from the register file. This enhances efficiency and minimizes delays.

Q: How does a Beta with a bad register file affect the program execution?

In this case, any data read directly from the register file will be zero. However, if the data is accessed via a bypass path, the correct value will be obtained.

Q: Why does a Beta without bypass paths result in stale values being read?

Without bypass paths, instructions might read stale values from the register file for their source operands. This occurs when the instructions updating the register have not completed by the time the dependent instruction reads the value.

Summary & Key Takeaways

  • There are four categories of discarded 5-stage pipelined Betas: fully functional with bypass and annulment logic, bad register file, without bypass paths, and without annulment of branch delay slots.

  • A test program is used to single-step through each Beta chip and determine its category by noting the address that the final JMP instruction loads into the PC.

  • The behavior of the program differs based on the category of the Beta chip, with differences in the values read from the register file and bypass paths.

Share This Summary 📚

Summarize YouTube Videos and Get Video Transcripts with 1-Click

Download browser extensions on:

Explore More Summaries from MIT OpenCourseWare 📚

Summarize YouTube Videos and Get Video Transcripts with 1-Click

Download browser extensions on: