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GR740
UDP when the IP packet has been fragmented. This condition is indicated by the IF bit in the receiver
descriptor and when set neither the TCP nor the UDP checksum error indications are valid.
14.5
MDIO Interface
The MDIO interface provides access to PHY configuration and status registers through a two-wire
interface which is included in the MII interface. The GRETH_GBIT provides full support for the
MDIO interface.
The MDIO interface can be used to access from 1 to 32 PHY containing 1 to 32 16-bit registers. A
read transfer i set up by writing the PHY and register addresses to the MDIO Control register and set-
ting the read bit. This caused the Busy bit to be set and the operation is finished when the Busy bit is
cleared. If the operation was successful the Linkfail bit is zero and the data field contains the read
data. An unsuccessful operation is indicated by the Linkfail bit being set. The data field is undefined
in this case.
A write operation is started by writing the 16-bit data, PHY address and register address to the MDIO
Control register and setting the write bit. The operation is finished when the busy bit is cleared and it
was successful if the Linkfail bit is zero.
14.5.1 PHY interrupts
The core also supports status change interrupts from the PHY. A level sensitive, active low, interrupt
signal can be connected on the eth{0,1}_mdint input. The PHY status change bit in the status register
is set each time an event is detected on this signal. If the PHY status interrupt enable bit is set at the
time of the event the core will also generate an interrupt on the AHB bus.
14.6
Ethernet Debug Communication Link (EDCL)
The EDCL provides access to an on-chip AHB bus through Ethernet. It uses the UDP, IP and ARP
protocols together with a custom application layer protocol. The application layer protocol uses an
ARQ algorithm to provide reliable AHB instruction transfers. Through this link, a read or write trans-
fer can be generated to any address on the AHB bus.
14.6.1 Operation
The EDCL receives packets in parallel with the MAC receive DMA channel. It uses a separate MAC
address which is used for distinguishing EDCL packets from packets destined to the MAC DMA
channel. The EDCL also has an IP address. Since ARP packets use the Ethernet broadcast address, the
IP-address must be used in this case to distinguish between EDCL ARP packets and those that should
go to the DMA-channel. Packets that are determined to be EDCL packets are not processed by the
receive DMA channel.
When the packets are checked to be correct, the AHB operation is performed. The operation is per-
formed with the same AHB master interface that the DMA-engines use. The replies are automatically
sent by the EDCL transmitter when the operation is finished. It shares the Ethernet transmitter with
the transmitter DMA-engine but has higher priority.
14.6.2 EDCL protocols
The EDCL accepts Ethernet frames containing IP or ARP data. ARP is handled according to the pro-
tocol specification with no exceptions.