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TT98.010
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1991-08-26
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Tech Tip #98.010
03/20/91
Problem: AMI Enterprise board: When using ramdrive in MSDOS 4.01
with the /e option, floppy drives cannot be accessed.
Reason: We have observed the following behavior:
* The floppy access problem happens only if the PS/2 mouse
support is disabled from the BIOS setup.
* If the PS/2 mouse support is enabled then there is no
problem accessing the A drive.
The EISA Architecture supports a fail safe timer NMI.
The AMI EISA BIOS handles the Enable/Disable of this
timer through INT 15 (AH)=C3 function.
This function is also used in the PS/2 50/60/70/80 to
Enable/Disable Watch Dog Timer. This funtion call uses
the PS/2 mouse data area. On the AMI EISA board this
area is defined only when the PS/2 mouse support is
enabled through the AMI EISA BIOS. This explains why
this problem does not appear as long as the PS/2 mouse
is enabled through AMI EISA BIOS setup.
When the PS/2 mouse support is disabled through the
setup, this data area is no longer available to the
INT15 function, though this funtion is still enabled.
Ramdrive uses this funtion call and corrupts the floppy
hardware interupt vector address.
Solution: The new release of the AMI EISA BIOS will disable the
INT15 function as soon as the PS/2 mouse support is
disabled through the setup.
In the mean time the system can still be used by keeping
the PS/2 mouse support enabled through the setup.