Datasheet

IdleSlope is the rate of change of increasing credit when waiting to transmit and must be less than the value of the
portT
ransmitRate.
IdleSlope is the rate of change of credit when waiting to transmit and must be less than the value of the
portTransmitRate.
The max value of IdleSlope (or sendSlope) is (portTransmitRate / bits_per_MII_Clock).
In case of 100 Mbps, maximum IdleSlope = (100 Mbps / 4) = 0x17D7840.
When this queue is transmitting the credit counter is decremented at the rate of sendSlope which is defined as
(portTransmitRate - IdleSlope). A queue can accumulate negative credit when transmitting which will hold off any
other transfers from that queue until credit returns 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.
The highest priority queue always has priority regardless of which queue has the most credit.
38.6.20 LPI Operation in the EMAC
It is best to use firmware to control LPI. LPI operation happens at the system level. Firmware gives maximum control
and flexibility of operation. LPI operation is straightforward and firmware should be capable of responding within the
required timeframes.
Autonegotiation:
1. Indicate EEE capability using next page autonegotiation.
For the transmit path:
1. If the link has been up for 1 second and there is nothing being transmitted, write to the TXLPIEN bit in the
Network Control register.
2. Wake up by clearing the TXLPIEN bit in the Network Control register.
For the receive path:
1. Enable RXLPISBC bit in GMAC_IER. The bit RXLPIS is set in Network Status Register triggering an interrupt.
2. Wait for an interrupt to indicate that LPI has been received.
3. Disable relevant parts of the receive path if desired.
4. The RXLPIS bit in Network Status Register gets cleared to indicate that regular idle has been received. This
triggers an interrupt.
5. Re-enable the receive path.
38.6.21 PHY Interface
Different PHY interfaces are supported by the Ethernet MAC:
• MII
• RMII
The MII interface is provided for 10/100 operation and uses txd[3:0] and rxd[3:0]. The RMII interface is provided for
10/100 operation and uses txd[1:0] and rxd[1:0].
38.6.22 10/100 Operation
The 10/100 Mbps speed bit in the Network Configuration register is used to select between 10 Mbps and 100 Mbps.
38.6.23 Jumbo Frames
The jumbo frames enable bit in the Network Configuration register allows the GMAC, in its default configuration, to
receive jumbo frames up to 10240 bytes in size. This operation does not form part of the IEEE 802.3 specification
and is normally disabled. When jumbo frames are enabled, frames received with a frame size greater than 10240
bytes are discarded.
SAM E70/S70/V70/V71 Family
GMAC - Ethernet MAC
© 2019 Microchip T
echnology Inc.
Datasheet
DS60001527D-page 601