LAN9730 Datasheet, PDF (61/222 Pages) SMSC Corporation – High-Speed Inter-Chip (HSIC) USB 2.0

LAN9730/LAN9730i
4.4.2.11 Stopping and Starting the Transmitter
To halt the transmitter, the host must set the Stop Transmitter (STOP_TX) bit in the TX_CFG register. The transmitter
will finish sending the current frame (if there is a frame transmission in progress). When the transmitter has received
the TX Status for the current frame, it will clear the STOP_TX and TX_ON bits in the TX_CFG register, and will pulse
TXSTOP_INT.
Once stopped, the host can optionally flush the TX FIFO, and can optionally disable the MAC by clearing TXEN. The
host must re-enable the transmitter by setting the TX_ON and TXEN bits. If there are frames pending in the TX FIFO
(i.e., the TX FIFO was not purged), the transmission will resume with this data.
Note: The TX Stop mechanism described here assumes that the MAC will return a status for every TX frame.
4.4.3 ARBITRATION
The FCT must arbitrate access to the RX and TX FIFOs to the URX, UTX, TLI RX, and TLI TX. Highest priority is always
given to the USB. The TLI RX/TX can be wait stated as frames buffering exists in the TLI (2 kB TX, 128 byte RX).
FCT strict priority order:
1. URX Request (Bulk-Out packet)
2. UTX Request (Bulk-In packet)
3. TLI RX (received Ethernet frame)
4. TLI TX (transmitted Ethernet frame)
Note: By nature of the USB bus and UDC operation, the URX and UTX do not request bandwidth simultaneously.
4.5 10/100 Ethernet MAC
The Ethernet Media Access Controller (MAC) incorporates the essential protocol requirements for operating an Ether-
net/IEEE 802.3-compliant node and provides an interface between the host subsystem and the internal Ethernet PHY.
The MAC can operate in either 100 Mbps or 10 Mbps mode.
The MAC operates in both half-duplex and full-duplex modes. When operating in half-duplex mode, the MAC complies
fully with Section 4 of ISO/IEC 8802-3 (ANSI/IEEE standard) and ANSI/IEEE 802.3 standards. When operating in full-
duplex mode, the MAC complies with IEEE 802.3x full-duplex operation standard.
The MAC provides programmable enhanced features designed to minimize host supervision, bus utilization, and pre-
or post-message processing. These features include the ability to disable retries after a collision, dynamic FCS (Frame
Check Sequence) generation on a frame-by-frame basis, automatic pad field insertion and deletion to enforce minimum
frame size attributes, layer 3 checksum calculation for transmit and receive operations, and automatic retransmission
and detection of collision frames.
The MAC can sustain transmission or reception of minimally-sized back-to-back packets at full line speed with an inter-
packet gap (IPG) of 9.6 microseconds for 10 Mbps and 0.96 microseconds for 100 Mbps.
The primary attributes of the MAC function are:
• Transmit and receive message data encapsulation
• Framing (frame boundary delimitation, frame synchronization)
• Error detection (physical medium transmission errors)
• Media access management
• Medium allocation (collision detection, except in full-duplex operation)
• Contention resolution (collision handling, except in full-duplex operation)
• Flow control during full-duplex mode
• Decoding of control frames (PAUSE command) and disabling the transmitter
• Generation of control frames
• Interface to the internal PHY and optional external PHY
• Checksum offload engine for calculation of layer 3 transmit and receive checksum
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DS00001946A-page 61