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Figure 20-2. Ethernet MAC and PHY Clock Structure
Internal PHY
MOSC
25 MHz
PTPCEN
Ethernet MAC
EN0RXIP
EN0RXIN
EN0TXOP
EN0TXON
RBIAS
EN0MDIO
EN0MDC
EN0INTRN
TX
RX
EN0LED2
EN0LED1
EN0LED0
Gated SYSCLK
PTP_REFCLK
MAC Control /
Status Registers
EMACCC
Tiva Cortex-M4
Microcontroller
20.3.2
DMA Controller
The Ethernet Controller's integrated DMA is used to optimize data transfer between the MAC and
system SRAM memory. The DMA has independent transmit and receive engines.
The DMA transmit engine transfers data from system memory to the Ethernet TX/RX Controller,
while the receive engine transfers data from the RX FIFO to the system memory. The controller
uses descriptors to efficiently move data from source to destination with minimal CPU intervention.
The DMA is designed for packet-oriented data transfers such as frames in Ethernet. Fixed burst
lengths of 1, 4, 8, or 16 words are supported along with re-initiation of bursts when retry or burst
termination responses occur. For a burst retry, if the remaining address count is greater than 1 and
the
RIB
bit in the
Ethernet MAC DMA Bus Mode (EMACDMABUSMOD)
register is clear, then the
transfer resends data in one continuous burst. When one transfer is left, it is done as a single burst
and the transaction is terminated immediately afterward. If the
RIB
bit in the
EMACDMABUSMOD
register is set, the DMA sends the remaining data in fixed burst sizes of 1, 4, 8, or 16 words.
The application may also choose between solely fixed bursts or mixed bursts by the DMA. If the
MB
bit is set and the
FB
bit is clear in the
EMACDMABUSMOD
register, then the DMA uses fixed bursts
for burst sizes less than 16 and a full, non-divided burst for lengths greater than 16. Fixed burst
lengths allow for more DMA bus arbitration with other masters. Maximum burst transfer lengths can
be programmed for both the receive and transmit channels of the DMA through the
PBL
,
RPBL
and
8xPBL
bit fields in the
EMACDMABUSMOD
register.
The DMA Controller requests a read transfer only when it can accept the received burst data
completely. Data read from the bus is always pushed into the DMA without any delay or busy cycles.
The DMA requests write transfers only when it has sufficient data to transfer the burst completely.
When operating in fixed burst length mode, the DMA interface continues to burst with dummy data
June 18, 2014
1410
Texas Instruments-Production Data
Ethernet Controller