GR740-UM-DS, Nov 2017, Version 1.7
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GR740
The MDIO interface is used for accessing configuration and status registers in one or more PHYs con-
nected to the MAC. The operation of this interface is also controlled through the APB interface.
The EDCL provides read and write access to an AHB bus through Ethernet. It uses the UDP, IP and
ARP protocols together with a custom application layer protocol to accomplish this. The EDCL con-
tains no user accessible registers and always runs in parallel with the DMA channels.
The Media Independent Interface (MII) and Gigabit Media Independent Interface (GMII) are used for
communicating with the PHY. More information can be found in section 14.7.
The EDCL and the DMA channels share the Ethernet receiver and transmitter. More information on
these functional units is provided in sections 14.3 - 14.6.
14.2.2 Protocol support
The GRETH_GBIT is implemented according to IEEE standard 802.3-2002. There is no support for
the optional control sublayer. This means that packets with type 0x8808 (the only currently defined
ctrl packets) are discarded.
14.2.3 Dedicated EDCL AHB master interface
The core has an additional master interface connected to the Debug AHB bus that can be used for the
EDCL. This master interface is enabled with the external signals GPIO[8] and GPIO[9]. These signals
are only sampled at reset and changes have no effect until the next reset. Note that the core can be
reset via the clock gating unit and that this will lead to the value of GPIO[9:8] being sampled. See sec-
tion 3.1 for further information on bootstrap signals.
14.3
Tx DMA interface
The transmitter DMA interface is used for transmitting data on an Ethernet network. The transmission
is done using descriptors located in memory.
14.3.1 Setting up a descriptor.
A single descriptor is shown in table 225 and 226. The number of bytes to be sent should be set in the
length field and the address field should point to the data. There are no alignment restrictions on the
address field. If the interrupt enable (IE) bit is set, an interrupt will be generated when the packet has
been sent (this requires that the transmitter interrupt bit in the control register is also set). The inter-
rupt will be generated regardless of whether the packet was transmitted successfully or not.
Table 225.
Address offset 0x0 - GRETH_GBIT transmit descriptor word 0
31
21 20 19 18 17 16 15 14 13 12 11 10
0
RESERVED
UC TC IC MO LC AL UE IE WR EN
LENGTH
31: 21
RESERVED
20
UDP checksum (UC) - Calculate and insert the UDP checksum for this packet. The checksum is only
inserted if an UDP packet is detected.
19
TCP checksum (TC) - Calculate and insert the TCP checksum for this packet. The checksum is only
inserted if an TCP packet is detected.
18
IP checksum (IC) - Calculate and insert the IP header checksum for this packet. The checksum is
only inserted if an IP packet is detected.
17
More (MO) - More descriptors should be fetched for this packet (Scatter Gather I/O).
16
Late collision (LC) - A late collision occurred during the transmission (1000 Mbit mode only).
15
Attempt limit error (AL) - The packet was not transmitted because the maximum number of
attempts was reached.
14
Underrun error (UE) - The packet was incorrectly transmitted due to a FIFO underrun error.