CHAPTER 21:Ethernet MAC
610
S6J3200 Series Hardware Manual Document Number: 002-04852 Rev. *G
4.
Wake up by clearing the LPI bit in the Network Control register.
For the receive path:
1.
Wait for an interrupt to indicate that LPI has been received.
2.
Disable relevant parts of the receive path if desired but keep the PCS and SerDes active.
3.
Wait for an interrupt to indicate that regular idle has been received and then re-enable the
receive path.
3.11.
IEEE Std 802.1Qav Support – Credit Based Shaping
A credit based shaping (CBS) algorithm is available on the two highest priority queues (Queue 3 (highest
priority), Queue 2) and is defined in IEEE Std 802.1Qav: Forwarding and Queuing Enhancements for
Time-Sensitive Streams (FQTSS). This allows traffic on these queues to be limited and to allow other
queues to transmit.
Traffic shaping is enabled via the CBS Control register. This enables a counter which stores the amount
of transmit ‘credit’, measured in bytes that a particular queue has. A queue may only transmit if it has
non-negative credit. If a queue has data to send, but is held off from doing as another queue is
transmitting, then credit will accumulate in the credit counter at the rate defined in the CBS IdleSlope
register for that queue (ETHERNETn_cbs_idleslope_q_a, ETHERNETn_cbs_idleslope_q_b). idleSlope
is the rate of change of credit when waiting to transmit and must be less than the value of the
portTransmitRate. When this queue is transmitting the credit counter is decremented at the rate of
sendSlope which is defined as the portTransmitRate – idleSlope. A queue can accumulate negative credit
when transmitting which will hold off any other transfers from that queue until credit retruns to a
non-negative value. No transfers are halted when a queue’s credit becomes negative, it will accumulate
negative credit until the transfer completes.
If both queues have positive credit, when the next queue to transfer is about to be selected, the queue
with the most positive credit will be allowed to transfer first. The queue with the largest positive credit is
the queue that had been prevented from transmitting for the longest time.
3.12.
PHY Interface
The Ethernet MAC supports only MII as PHY interface.
3.13.
Jumbo Frames
The jumbo frames enable bit in the Network Configuration register (bit 3) allows the Ethernet MAC in its
initial state to receive jumbo frames up to 10240 bytes in size. This operation is not part of IEEE Std 802.3
specification and is normally disabled. When jumbo frames are enabled, frames received with a frame
size greater than 10240 bytes are discarded.
The jumbo frames maximum length can be controlled using the Jumbo-Frame Maximum Length register.
Its initial value is 2800
h
which corresponds to 10240 bytes.
Note: The Jumbo-Frame Maximum Length register must be set to greater 1536 bytes (600
h
) when control
bit receive_1536_byte_frames in the Network Configuration register (bit 8) is set to “1”.
Summary of Contents for S6J3200 Series
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