MPC8540 datasheet(1164/1302 Pages) FREESCALE

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MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

21-24

Freescale Semiconductor

10/100 Fast Ethernet Controller

Table 21-11 describes the fields of the FIFO_TX_THR register.

21.5.3.2.3 FIFO Transmit Starve Register (FIFO_TX_STARVE)

The purpose of the starve register is to inform the system of extremely imminent underrun

conditions. It represents the numerical SRAM entry (0–255 for 1-Kbyte FIFO) to trigger the starve

function. If the used entry count in the FIFO is less than or equal to the starve register, a starve

alert is triggered. This triggered condition is used to throttle back the OCN2CU interface at the

e500 coherency module (ECM), to change the Tx transaction priority. This register is read/write

by software. Figure 21-13 describes the definition for the FIFO_TX_STARVE register.

Table 21-12 describes the fields of the FIFO_TX_STARVE register.

21.5.3.2.4 FIFO Transmit Starve Shutoff Register

(FIFO_TX_STARVE_SHUTOFF)

The starve shutoff registers contains the watermark level to be used for coming out of the starve

state. If the starve state is in effect and the number of valid entries in the FIFO becomes greater

than or equal to the value in the FIFO_TX_STARVE_SHUTOFF register, the starve condition

Table 21-11. FIFO_TX_THR Field Descriptions

Bits

Name

Description

0–23

—

Reserved

24–31

FIFO_TX_THR FIFO transmit threshold. Marks the number of entries in the transmit FIFO that when

reached triggers the unloading of frame data into the MAC. If the FIFO Tx used entry count

is equal to or greater than FIFO_TX_THR, frame transmission request is sent to the MAC.

23 24

R 00000000

000000000000000

FIFO_TX_STARVE

Reset

0000_0000_0000_0000_0000_0000_0010_0000

Offset

0x2_6098

Figure 21-13. FIFO_TX_STARVE Register Definition

Table 21-12. FIFO_TX_STARVE Field Descriptions

Bits

Name

Description

0–23

—

Reserved

24–31

FIFO_TX_STARVE

FIFO transmit starve. Indicates the value to trigger the transmit starve function. It

triggers once the FIFO transmit used entry count is less than or equal to the FIFO Tx

starve. The starve state turns off when the FIFO Tx used entry count becomes greater

than or equal to the FIFO Tx starve shutoff register.

MPC8540 Datasheet(PDF) 1164 Page - Freescale Semiconductor, Inc

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