Re: LINUX is obsolete
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Re: LINUX is obsolete
In article <12605@star.cs.vu.nl> ast@cs.vu.nl (Andy Tanenbaum) writes:
>In article <1992Jan29.141212.29636@epas.toronto.edu> meggin@epas.utoronto.ca (David Megginson) writes:
>>
>>Why does the
>>Intel architecture _not_ allow drivers to be independent programs?
>
>The drivers have to read and write the device registers in I/O space, and
>this cannot be done in user mode on the 286 and 386. If it were possible
>to do I/O in a protected way in user space, all the I/O tasks could have
>been user programs, like FS and MM.
>
>Andy Tanenbaum (ast@cs.vu.nl)
Every 386 TSS has an iopermission bitmap. If the CPL is of a lower priveledge
level than IOPL, the io permissions bitmap is consulted, allowing protection
on a port by port basis.