ksz8851-mql Micrel Semiconductor, ksz8851-mql Datasheet - Page 33

• Manufacturer Part Number: ksz8851-mql
• Description: Single-port Ethernet Mac Controller With 8/16-bit Or 32-bit Non-pci Interface
• Manufacturer: Micrel Semiconductor

Queue Management Unit (QMU)
The Queue Management Unit (QMU) manages packet traffic between the MAC/PHY interface and the system host. It has
built-in packet memory for receive and transmit functions called TXQ (Transmit Queue) and RXQ (Receive Queue). Each
queue contains 12KB for RXQ and 6KB for TXQ of memory with back-to-back, non-blocking frame transfer performance.
It provides a group of control registers for system control, frame status registers for current packet transmit/receive status,
and interrupts to inform the host of the real time TX/RX status.
Transmit Queue (TXQ) Frame Format
The frame format for the transmit queue is shown in the following Table 5. The first word contains the control information
for the frame to transmit. The second word is used to specify the total number of bytes of the frame. The packet data
follows. The packet data area holds the frame itself. It may or may not include the CRC checksum depending upon
whether hardware CRC checksum generation is enabled in TXCR (bit 1) register.
Multiple frames can be pipelined in both the transmit queue and receive queue as long as there is enough queue memory,
thus avoiding overrun. For each transmitted frame, the transmit status information for the frame is located in the TXSR
(0x72) register.
Since multiple packets can be pipelined into the TX packet memory for transmit, the transmit status reflects the status of
the packet that is currently being transferred on the MAC interface, which may or may not be the last queued packet in the
TX queue.
The transmit control word is the first 16-bit word in the TX packet memory, followed by a 16-bit byte count. It must be word
aligned. Each control word corresponds to one TX packet. Table 6 gives the transmit control word bit fields.
February 2009
Micrel, Inc.
Packet Memory
Address Offset
0
2
4 - up
Figure 7. KSZ8851M 8-Bit, 16-Bit, and 32-Bit Data Bus Connections
Table 5. Frame Format for Transmit Queue
Bit 15
2
Control Word (High byte and low byte need
to swap in Big-Endian mode)
Byte Count (High byte and low byte need to
swap in Big-Endian mode)
Transmit Packet Data
(maximum size is 2000)
nd
Byte
33
1
st
Bit 0
Byte
KSZ8851-16/32 MQL/MQLI
M9999-021309-1.1