TNETX3150 datasheet(45/113 Pages) TI1

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TNETX3150/TNETX3150A

ThunderSWITCH™ 15-PORT 10-/100-MBIT/S ETHERNET™ SWITCH

SPWS027F – FEBRUARY 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

transmit queue-length registers at 0x2*N + 0x0080 through 0x2*N + 0x0081

DIO ADDRESS

Transmit queue 1 length

Transmit queue 0 length

0x80

Transmit queue 3 length

Transmit queue 2 length

0x84

Transmit queue 5 length

Transmit queue 4 length

0x88

Transmit queue 7 length

Transmit queue 6 length

0x8C

Transmit queue 9 length

Transmit queue 8 length

0x90

Transmit queue 11 length

Transmit queue 10 length

0x94

Transmit queue 13 length

Transmit queue 12 length

0x98

Reserved

Transmit queue 14 length

0x9C

Reserved

NMON

XCTRL/SIO

Revision register

0xA0

Transmit queues use a residual queue length to control their behavior. Its value indicates how many more

buffers can be added to the queue, rather than how many buffers are on the queue. This is an advantage

because it is easy to detect that the queue is full (length goes negative) and can be adjusted dynamically (2’s

complement addition to the length).

After reset, all transmit queue-length registers are initialized to zero. These registers are part of the address

range that can be read from the EEPROM. The first time value written to the transmit queue-length registers

is the initial value. When the user writes again, the value entered is added as a signed 16-bit integer to the current

value.

As frames are placed on the queue, the transmit queue length is decremented by the number of buffers queued.

Should the transmit queue length become negative (most-significant bit set and the queue is full), no new frames

are added until the length becomes positive by the transmission of buffers. Since a maximum-size frame (1518

bytes) is 24 buffers long, and whole frames are queued based on the current transmit queue-length value, the

queue can consume 23 more buffers than the initial residual length (i.e., if the transmit queue is set to length

= 1, a full-size Ethernet frame still can be queued). As buffers are transmitted, the transmit queue length is

incremented.

The transmit queue registers are used to initialize, alter, and provide status on transmit queue lengths. They

are used in three different ways:

To assign initial transmit queue-length value. The value in the register is used as its initial value when the

first frame is put on the queue.

To indicate current transmit queue-length value. The register is loaded with the transmit queue-length value

when it is updated.

To adjust transmit queue length.

After transmit queue initialization, a value written to this register is added to the current transmit queue-length

value the next time it is updated. The update bit in port status is used to detect initialization or that an update

operation is complete. The operation is a 16-bit addition, allowing the current queue length to be increased or

decreased. The update operation is enabled only when the most-significant byte of the register (15–8) is written

to prevent possible length corruption. Ensure that length bytes are always written least-significant byte first.

TNETX3150 数据表(PDF) 45 Page - Texas Instruments

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