Alto
Hardware Manual
EOCLOC
=
606B:
EOPLOC
=
607B:
EHLOC
=
610B:
Section
7:
Ethernet
50
Output fount location. The emulator program should
put
the size
of
the
output buffer (in words) into this location before starting the transmitter.
By
convention, packets should not be substantially longer than 256 words.
Output Qointer location. The emulator program should
put
a pointer to the
beginning
of
the output buffer into this location before starting the
transmitter.
Host address location. This location must contain zero
in
the left byte and
the host address in the rigbt byte. The microcode matches this
host
address
against the first byte of a passing packet to decide whether
to
accept it.
SIc)
passes commands to the interface and returns the host address
of
the Alto. Commands to
the.
Ethernet interface are encoded in the
two
low
order bits
of
ACO
and have the following meaning (the
remaining bits
of
ACO
may
be
interpreted
by
other devices and thus should
be
zero):
AcO[14-15]:
0 Do nothing
1 Start the transmitter
2 Start the receiver
3 Reset the interface and microcode.
The host address, returned in
AcO[8-15]
by
SIO,
is
set by
wires
on the Alto backpanel. This number is
normally put in
EHLOC
thereby causing packets
with
destination addresses matching the address set with
the wires to be accepted by the receiver. For more on addressing, see below.
Upon completion
of
a command,
EPLOC
contains the status
of
the microcode
in
the left byte and the
status
of
the interface in the right byte. The possible values
of
the microcode status byte, EPLoc[0-7],
and their meanings are:
EPLoc[0-7]
=
0:
EPLOc[0-7]
=
1:
EPLOc[0-7]
=
2:
Input done.
If
the hardware status byte
is
377B,
the interface believes the
packet
was
received without error.
Output done.
If
the hardware status byte is
377B,
the interface believes the
packet
was
sent without error. The number
of
collisions experienced while
sending the packet
is
log2(ELLOCl2
+ 1)-1.
Input buffer overrun. The received packet
was
longer than the buffer, and
the excess words
were
lost. Buffer overrun causes an early exit from the
microcode input main loop,
so
it
is
likely that the
CRC
error and Jncomplete
,!ransmission bits in the hardware status byte will
be
set.
EPLoc[O-7]
=
3:
Load overflow. The transmitter experienced
16
consecutive collisions
(assuming
ELLOC
was
zeroed before starting the transmitter) while trying to
transmit the packet described
by
EOPLOC
and
EOCLOC.
ELLOC[O]
will
be
one.
EPLoc[0-7]
=
4:
The command (input or output) specified a zero length buffer.
EPLoc[0-7]
=
5:
Reset. Generally indicates that a reset command
(SIO
with
AcO[14-15]
= 3)
was
issued to the interface when it
was
idle or any command was issued
when it
was
not
idle.
EPLOc[O-7]
=
6:
Microcode branch conditions that should never happen cause this code to be
posted
if
they do happen.
EPLOC[O-7]
=
7-377B:
The microcode does not generate these values for status.
Note that the microcode statuses are
small integers and not individual bits
as
in the interface status byte.
Bits
in the interface status byte,
EPLOc[8-15],
are low
true.
When zero, their meanings are:
To Next Page
Loading...
Need help?
General
