KSZ8851-16MLLJ_10 MICREL [Micrel Semiconductor], KSZ8851-16MLLJ_10 Datasheet - Page 28

• Manufacturer Part Number: KSZ8851-16MLLJ_10
• Description: Single-Port Ethernet MAC Controller with 8-Bit or 16-Bit Non-PCI Interface
• Manufacturer: MICREL [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.
The transmit Byte Count specifies the total number of bytes to be transmitted from the TXQ. Its format is given in Table 7.
March 2010
Bit
15
14-6
5-0
Micrel, Inc.
Description
TXIC Transmit Interrupt on Completion
When this bit is set, the KSZ8851-16MLLJ sets the transmit interrupt after the present frame has been transmitted.
Reserved.
TXFID Transmit Frame ID
This field specifies the frame ID that is used to identify the frame and its associated status information in the transmit status
register.
Packet Memory Address Offset
4 - up
0
2
Table 5. Frame Format for Transmit Queue
Table 6. Transmit Control Word Bit Fields
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
28
1
st
Byte
Bit 0
M9999-030210-1.0
KSZ8851-16MLLJ