Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
45-10
Freescale Semiconductor
simultaneously, the CPM wins the first access. If both continue to request the SDMA hardware, control
alternates between the two.
Figure 45-3. SDMA Bus Arbitration
The priority of the SDMA on the U-bus is set to 6, described in
Section 45.2.12.1, “SDMA Configuration
Register (SDCR).”
45.2.12 The SDMA Registers
The SDMA channels share a configuration register, address register, and status register, and are controlled
by the configuration of the SCCs, SMCs, SPI, and I
2
C controllers.
45.2.12.1 SDMA Configuration Register (SDCR)
The SDMA configuration register (SDCR) interacts with the DMA controllers in the FEC, see
Section 19.2.1, “SDMA Configuration Register (SDCR).”
45.3
Programming Model
The FEC software model is similar to that used by the 10-Mbps Ethernet implemented on the CPM. To
support higher data rates, the FEC has a different internal architecture, which changes the programming
model slightly. However, efforts have been taken to minimize the differences required by the interrupt
handlers. The FEC’s registers are very different from those of the CPM-based internal Ethernet controller.
The FEC is programmed by a combination of control/status registers (CSRs) and BDs. The CSRs are used
for mode control and to extract global status information. The BDs are used to pass data buffers and related
buffer information between hardware and software.
Some registers are located in on-chip RAM. All on-chip registers, whether located in RAM or in hardware,
must be accessed using big-endian mode. Therefore, descriptions in this chapter assume big-endian byte
ordering. There is no support for little-endian in the FEC.
CLK
TS
TA
Other cycle
SDMA cycle
Other cycle
SDMA internally
requests the bus
Summary of Contents for PowerQUICC MPC870
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