4 ms·
It's even worse than that. If it was just the CPU... It also simulate an old keyboard controller for the purpose of enabling the A20 gate which enables an addr
by ithkuil 3y ago
It's even worse than that. If it was just the CPU...
It also simulate an old keyboard controller for the purpose of enabling the A20 gate which enables an address line.
https://en.m.wikipedia.org/wiki/A20_line https://en.m.wikipedia.org/wiki/A20_line
- armada651 3y agoSupport for the A20 gate was actually already dropped as per the article you linked: > Intel no longer supports the A20 gate, starting with Haswell.
- jylam 3y agoIt was not needed anymore in Haswell, but the support was still there. It isn't supported at all anymore.
- deaddodo 3y agoThe A20 gate was deprecated (and made software-based) in Nehalem, then was removed completely in Haswell. It's never been a feature of the Zen µarch(s).
- bonzini 3y agoEmulation of the keyboard controller is done by the firmware. The processor's support for A20 was tied to port 92h.
- Dwedit 3y agoThe A20 line was famously used to hack the original XBox. By clearing A20, you prevent the XBox from booting from the hidden ROM, and it boots from regular flash ROM instead. Some great videos about that on YouTube if you want to look.