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Alto Hardware Manual
Section 7: Ethernet
54
data word once every 5.44 microseconds on the average. The microcode signals the hardware when the
main memory buffer is empty and waits for the hardware to terminate; it then posts status.
A reset cominand (SIO with AcO[14-15] = 3) will always bring the interface back to a reset state. If the
receiver was on, it is stopped even if a packet was pouring into memory. If the transmitter was on, it is
stopped, even if it was in the middle of transmitting a packet (the result to the receiver of the interrupted
packet will almost certainly be an incomplete transmission and incorrect CRC). - Status will immediately
be -posted in EPLOC: the microcode will post the reset status (5) in the microcode status byte, and the
hardware will post the conditions at the time of the reset in the hardware status byte. The contents of
the ECNTR R register will be deposited in EELOC, and the contents of EBLOC will be ORed into
NWW,
possibly causing interrupts. After doing this, the interface and microcode are reset and ready for another
command.
The task specific microcode functions for the Ethernet interface are summarized below.
EIDFCT
*
BS = 4
Input Data function.
Gates the contents of the FIFO to Bus[O-15], and
increments the read pointer at the end of the cycle.
EILFCT
*
Fl=13B
Input Look Function. Gates the contents of the FIFO to BUS[O-15] but does
not increment the read pointer.
EPFCT
Fl = 14B
Post Function. Gates interface status to Bus[S-15]. Resets the interface at
the end of the cycle.
-
EWFCT
EODFCT
EOSFCT
ERBFCT
EEFCT
EBFCT
ECBFCT
EISFCT
Fl=15B
F2=10B
F2=llB
F2=12B
F2=13B
F2=14B
F2=15B
F2=16B
Countdown Wakeup function.
Sets a flip flop in the interface that will
cause a wakeup to the Ether task on the next tick of SWAKMRT.
This
function must be issued in the instruction aftet -a TASK.
The· resulting
wakeup is cleared when the Ether task next runs,
-
-
-
Output Data fun£!ion. -Loads theHFo-from-Bus[O-15], then increments the
write pointer at the end of the cycle.
Output §tart funf!ion. Sets the OBUSY flip flop in the interface, starting
data wakeups to fill the FIFO for output. When the FIFO is full, or EEFct has
been issued, the interface will wait for silence on the Ether and begin
transmitting.
Reset Branch Function. This command dispatch function merges the ICMD
and
00.10
flip flops, into NEXT[6-7].
These flip flops are the means of
communication between the emulator task and the Ethernet task.
The
emulator task sets them from BUS[14-15] with the STARTF function, causing
the Ethernet task to wakeup, dispatch on them and then reset them with
EPFCT.
End of transmission Function. This function is issued when all of the main
memory output buffer has been transferred to the FIFO.
EEFCT disables
further data wakeups.
Branch Function. ORs a one into NEXT[7] if an input data late is detected,
or an SID with AcO[14:1S] non-zero is issued, or if the transmitter or receiver
goes done.
ORs a one into
NEXT[6]
if a collision is detected.
Countdown !!ranch funf!ion.oRs a one into NEXT[7] if the FIFO is not
empty.
Input Start Function. Sets the !Busy flip flop in the interface, causing it to
hunt fur the beginning of a packet: ·silence -on the Ether followed by a
transition.
When the interface has collected two words, it will begin
generating data wakeups to the microcode.
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