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Programming the Ethernet controller (view source)
Revision as of 18:41, 20 July 2007
, 18:41, 20 July 2007no edit summary
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Anything other than the three defined packets is considered a bad packet and is discarded in the CP2200/1 before transitioning back to state 010. An "R" packet obtains the reset mask from the second byte then discards the packet before transitioning to state 000. State 000 assumes that the reset mask is held, so this output needs to be latched in place until the next time this block activates. A query has no switches or masks on it, so a "Q" packet will be discarded from the CP2200/1 before continuing on. A "P" packet has a large amount of data attached to it, so that is the only packet not discarded before continuing to the next state. This allows later states to access the packet data, but also puts on those later states the responsibility for discarding the packet once finished with it.
Anything other than the three defined packets is considered a bad packet and is discarded in the CP2200/1 before transitioning back to state 010. An "R" packet obtains the reset mask from the second byte then discards the packet before transitioning to state 000. State 000 assumes that the reset mask is held, so this output needs to be latched in place until the next time this block activates. A query has no switches or masks on it, so a "Q" packet will be discarded from the CP2200/1 before continuing on. A "P" packet has a large amount of data attached to it, so that is the only packet not discarded before continuing to the next state. This allows later states to access the packet data, but also puts on those later states the responsibility for discarding the packet once finished with it.
inputs
* ''Clk'': clock
* ''/Rst'': asynchronous, active-low reset
* ''State'': 3-bit state value
* - transceiver control lines -
internal signals
* ''S_En'': state enable, ''S_En'' <= not (''St(2)'' or ''St(1)'' or ''St(0)'')
* ''Go'': when ''S_En'' goes high ''Go'' pulses for one cycle
blocks
* '''MAC Filter'''
** This block checks that the MAC address in the packet destination field is the same as the MAC address of the board. If not the packet is discarded, if so then the MAC data (destination and source MAC address, packet length) are discarded and processing continues.
** inputs
*** ''Clk'': clock
*** ''/Rst'': asynchronous, active-low reset
*** ''Go'': pulse to begin
*** - transceiver control lines -
** outputs
*** ''Discard'': pulse to State Advance to discard packet and return to 010
*** ''Continue'': pulse to Switch to continue processing
*** - transceiver control lines -
* '''Switch'''
** This block reads the first data byte of the packet and uses it as a switch to direct the state machine to the appropriate next step.
** inputs
*** ''Clk'': clock
*** ''/Rst'': asynchronous, active-low reset
*** ''Go'': pulse to begin
*** - transceiver control lines -
** outputs
*** ''Discard'': pulse to State Advance to discard packet and return to 010
*** ''Reset_000'': pulse to State Advance to discard packet and go to 000
*** ''Query'': pulse to State Advance to discard packet and go to 100
*** ''Program'': pulse to State Advance to keep packet and go to 110
*** - transceiver control lines -
* '''State Advance'''
** This block has several ''Go'' lines and based on which is pulsed the next state is set up by loading a new state value into the state register. It also discards packets other than "P".
** inputs
*** ''Clk'': clock
*** ''/Rst'': asynchronous, active-low reset
*** ''Discard'': pulse to discard packet and return to 010
*** ''Reset_000'': pulse to discard packet and go to 000
*** ''Query'': pulse to discard packet and go to 100
*** ''Program'': pulse to keep packet and go to 110
*** - transceiver control lines -
** outputs
*** ''Done'': pulse to signal completion; connects to state register enable
*** ''New_St'': new state to load to state register; goes to 000, 010, 100, or 110 when ''Done'' is high depending on switching
*** - transceiver control lines -
=== (100) Poll Status ===
=== (100) Poll Status ===