Fast Ethernet Controllers (FEC0 and FEC1)
26-39
Freescale Semiconductor
26.5.8
FEC Frame Reception
The FEC receivers work with almost no intervention from the host and can perform address recognition,
CRC checking, short frame checking, and maximum frame length checking. The Ethernet controller
receives serial data lsb first.
When the driver enables the FEC receiver by setting ECR
n
[ETHER_EN], it immediately starts processing
receive frames. When FEC
n
_RXDV is asserted, the receiver first checks for a valid PA/SFD header. If the
PA/SFD is valid, it is stripped and the receiver processes the frame. If a valid PA/SFD is not found, the
frame is ignored.
In serial mode, the first 16 bit times of RX_D0 following assertion of FEC
n
_RXDV are ignored.
Following the first 16 bit times, the data sequence is checked for alternating 1/0s. If a 11 or 00 data
sequence is detected during bit times 17 to 21, the remainder of the frame is ignored. After bit time 21, the
data sequence is monitored for a valid SFD (11). If a 00 is detected, the frame is rejected. When a 11 is
detected, the PA/SFD sequence is complete.
In MII mode, the receiver checks for at least one byte matching the SFD. Zero or more PA bytes may occur,
but if a 00 bit sequence is detected prior to the SFD byte, the frame is ignored.
After the first 6 bytes of the frame are received, the FEC performs address recognition on the frame.
After a collision window (64 bytes) of data is received and if address recognition has not rejected the
frame, the receive FIFO signals the frame is accepted and may be passed on to the DMA. If the frame is a
runt (due to collision) or is rejected by address recognition, the receive FIFO is notified to reject the frame.
Therefore, no collision fragments are presented to you except late collisions, which indicate serious LAN
problems.
During reception, the Ethernet controller checks for various error conditions and after the entire frame is
written into the FIFO, a 32-bit frame status word is written into the FIFO. This status word contains the
M, BC, MC, LG, NO, CR, OV, and TR status bits, and the frame length. See
for more details.
Receive buffer (RXB) and frame interrupts (RFINT) may be generated if enabled by the EIMR
n
register.
A receive error interrupt is a babbling receiver error (BABR). Receive frames are not truncated if they
exceed the max frame length (MAX_FL); however, the BABR interrupt occurs and the LG bit in the
receive buffer descriptor (RxBD
n
) is set. See
Section 26.5.1.2, “Ethernet Receive Buffer Descriptors
for more details.
When the receive frame is complete, the FEC sets the L-bit in the RxBD
n
, writes the other frame status
bits into the RxBD
n
, and clears the E-bit. The Ethernet controller next generates a maskable interrupt
(RFINT bit in EIR
n
, maskable by RFIEN bit in EIMR
n
), indicating that a frame is received and is in
memory. The Ethernet controller then waits for a new frame.
26.5.9
Ethernet Address Recognition
The FECs filter the received frames based on destination address (DA) type — individual (unicast), group
(multicast), or broadcast (all-ones group address). The difference between an individual address and a
Summary of Contents for MCF54455
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Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
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