i86.cpp: Need different EA execution times per CPU variant (808x/80186/80286) #14632
+54
−31
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
CPU variant to the next. On the 286, it's effectively free, unless two additions are required, in which case it takes 1 cycle. On the 8088/8086 on the other hand, it can take up to 12 cycles. There needs to be a different set of timings for each CPU variant. I tested on a 286 system (att6300p) with https://thandor.net/benchmark/36, and the score went from 29 to 46 - almost a 60% speedup! Also added a few minor cycle count fixes.
cracyc
approved these changes
Dec 3, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The 286 is running a lot slower than it should since it's being "billed" for effective address calculations at 808x rates. A benchmark I ran on att6300p (https://thandor.net/benchmark/36) shows a score increase from 29 to 46 with this change applied.
I discovered this issue because one of the tests on the 6300 Plus diagnostics disk was failing, since the test was taking longer than expected. There's a possibility that the POST on some machines could fail in a similar way.