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Section A:
System interface
A.3. I/O device assignments
With
EOS,
I/0 device assignment has been completely
redesigned.
Five
logical devices have been defined. These devices are:
Console Input
for functions l, 6. 10,
and
l l
Console Output
for functions 2, 6, 9,
and lll
Aux Device Input
for functions 3
and
7
Aux Device Output
for functions 4
and
B
List Output
for functions
5
and 112
Physical
devices
may be freely defined by the
system
implementor.
A
device table is constructed to describe the properties of the devices as
follows:
DB
DB
DB
'NAME
ATTRIB
BAUD
device name, 6 Bytes
attribute byte
software adjustable Baud rate
The attribute byte is a bit vector with the following meanings:
Bit 0 set - Device
can
perform input
Bit
l
set
-
Device
can
perform output
Bit
2
set - Baud rate is software-adjustable
Bit 3 set
-
Device uses CTS
-
protocol
Bit 4 set
-
Device uses XON/XOFF
-
protocol
All
physical I/0 devices except for the disk drives are defined in this
table.
The
devices are numbered internally,
the first table entry
is
number
~.
the second one number l, and so forth. Each logical device has
a 16-bit vector associated for up to 16 physical devices, where the most
significant bit corresponds to physical device
~.
the second to physical
device 1,
and so on. To map a
physical device to a logical, simply the
corresponding bit in its vector is set.
This concept allows for more than one physical device being allocated to
a logical device by setting more than one bit in its mapping vector.
If
so, the system reaction is as follows:
When an input device is referred to,
all mapped physical devices from
~
upwards are tested for a pending character.
The first device ready
for
input is then read by EOS.
EOS System manual
Daeumling & Zimmermann
Page 5
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