USB97C100QFP datasheet(40/64 Pages) SMSC

40 / 64 page

SMSC DS – USB97C100

Page 40

Rev. 01/03/2001

MMU Free Pages Register

MMU Free Pages bits, and a global NAK_ALLRX (this can only NACK OUT and Bulk packets) control bit for the

firmware to view the real time status of the 32 page allocation bits. This allows the MCU to set NAK_ALLRX which

would inhibit the SIE from asking the SIEDMA to allocate packets, MCU checks how many pages are left, issue an

allocate if enough are free, and then release the SIE/SIEDMA. For the current design, the number of free pages

would range from 0x00 to 0x1F (32) pages left unallocated.

The indication of pages free may be invalid during an allocation or deallocation.

Table 66 - Pages Free In The MMU

PAGS_FREE

(0x7F56 - RESET=0x20)

PAGES FREE IN THE MMU

BIT

NAME

R/W

DESCRIPTION

NAK_ALLRX

R/W

NACK All received packets

0 = Normal Operation (Default)

1 = NACK all RX packets

Reserved

[5:0]

PAGS_FREE

These bits indicate the number of free pages in the MMU.

Notes:

Firmware can set a NAK_ALLRX bit to inhibit the SIE from asking the SIEDMA to allocate any pages while the

MCU is observing the page free bits.

This register is used to indicate how many pages are left in many situations, including after an RX_OVRN,

before a multi-packet allocation, etc. This eliminates the possibility of a failed allocation, simplifying software

without adding additional hardware to abort an allocation.

16 BYTE DEEP TX COMPLETION FIFO REGISTER

Table 67 - TX Management Register 2

TX_MGMT

(0x7F57 - RESET=0x80)

TX Management Register

BIT

NAME

R/W

DESCRIPTION

CTX_EMTY

Completed TX FIFO empty status

0 = Has one or more TX packet

1 = Empty

CTX_FULL

Completed TX FIFO full status

0 = Not FULL

1 = FULL

Reserved

[4:0]

CTX_FIFO

This is the data port for the 16 deep TX completion FIFO. This

FIFO is automatically updated by hardware with the last

successfully completed transmit packet. It is the responsibility of

software to ensure that this FIFO never overflows and/or becomes

full.

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