[SeaBIOS] ohci bulk?

H. Peter Anvin hpa at zytor.com
Thu Sep 23 05:09:06 CEST 2010

On 09/22/2010 07:05 PM, Kevin O'Connor wrote:
>> Actually you can switch to protected mode and turn the page tables on if
>> you want.
> That's a good idea.  Though it still sounds tricky to handle page
> faults.

Yes, probably.  On the other hand, if the BIOS low-level hardware
drivers are executed in V86 mode without a 1:1 mapping you're pretty
much dead anyway (since DMA would be all wrong.)

>>> I didn't think there was a way for the user code to know it was
>>> running in vm86 mode - I thought it appeared just like regular
>>> real-mode.  One could try to go into protected mode and try to catch
>>> the failure, but I'd guess most OSs that run code in vm86 mode would
>>> trap and abort in that situation.
>> No, the SMSW instruction can be used to distinguish protected mode and
>> therefore V86 mode.
> Thanks.  Do you know of a way to backup the hidden segment registers?
> The BIOS can be invoked in real mode or bigreal mode.  I didn't see a
> way for the BIOS to determine this so that it can properly return in
> the same mode (real vs bigreal).

There isn't one (other than binary search of the faulting space) except SMM.


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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