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2.2
Memory Map
The EMAC peripheral includes internal memory that is used to hold information about the Ethernet
packets received and transmitted. This internal RAM is 2K
read from the EMAC internal memory by either the EMAC or the CPU. It is used to store buffer descriptors
that are 4-words (16-bytes) deep. This 8K local memory holds enough information to transfer up to 512
Ethernet packets without CPU intervention.
The packet buffer descriptors can also be placed in the internal processor memory (L2), or in EMIF
memory (DDR). There are some tradeoffs in terms of cache performance and throughput when
descriptors are placed in the system memory, versus when they are placed in the EMAC's internal
memory. Cache performance is improved when the buffer descriptors are placed in internal memory.
However, the EMAC throughput is better when the descriptors are placed in the local EMAC RAM.
2.3
Signal Descriptions
The DM646x DMSoC supports both MII interface (for 10/100 Mbps operation) and GMII interface (for
10/100/1000 Mbps) operation.
2.3.1
Media Independent Interface (MII) Connections
Figure 2
shows a device with integrated EMAC and MDIO interfaced via a MII connection. The EMAC
module does not include a transmit error (MTXER) pin. In the case of transmit error, CRC inversion is
used to negate the validity of the transmitted frame.
The individual EMAC and MDIO signals for the MII interface are summarized in
information, refer to either the IEEE 802.3 standard or ISO/IEC 8802-3:2000(E).
System
SPRUEQ6 – December 2007
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Figure 2. Ethernet Configuration—MII Connections
MTCLK
MTXD(7−0)
MTXEN
MCOL
MCRS
MRCLK
core
MRXD(7−0)
MRXDV
MRXER
MDCLK
MDIO
Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO)
32 bits in size. Data can be written to and
Table
2.5 MHz,
25 MHz or
125 MHz
Physical
layer
Transformer
device
(PHY)
RJ−45
Architecture
1. For more
15
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