USB97C102 datasheet(46/80 Pages) SMSC

46 / 80 page

SMSC DS – USB97C102

Page 46

Rev. 03/23/2000

MMU COMMAND Bits 7, 6, and 5 Description:

000

NOOP, No operation

001

Allocate Memory : N3-0 specify how many 128 byte pages to allocate for that packet (up to 10 pages

allowed (1280 bytes) per packet.) Immediately generates a "FAILED" code at the ARR and the code is

cleared when complete. Can generate an ALLOC interrupt to MCU upon completion. When an allocation

request cannot be completed due to insufficient memory, the FAILED bit in the ARR will remain set. Any

subsequent release of memory pages (by either the MMUCR or the SIEDMA) will cause the MMUCR to

automatically continue the allocate command until all requested pages have been successfully allocated.

Software should never issue another allocate command until the previous allocate command has been

successfully completed.

010

RESET MMU : Frees all buffer RAM, clears interrupts, and resets queue pointers.

011

Remove Packet from top of RX Queue : To be issued after MCU has completed processing the packet

number at the RXFIFO.

100

Remove and Release Top of RXFIFO : Same as (011), but also frees all memory used by the packet. This

command is especially useful as a quick way to "ignore" bad packets.

101

Release specific Packet : Frees all pages allocated to the packet specified in the PNR.

110

Enqueue Packet into Endpoint x : Places the Packet number indicated by the PNR register in the transmit

queue of the endpoint pointed to by the MMUTX_SEL register. The MMUTX_SEL register must be written

before this command is issued.

111

Reset TX Endpoint x : Resets the TX FIFO holding the packet numbers awaiting transmission and the

TXFIFO_STAT bits of the endpoint pointed to by the MMUTX_SEL register. The MMUTX_SEL register must

be written before this command is issued. This command does not release any memory allocated to packets

that are dequeued.

Table 83 - Allocation Result Register

ARR

(0x7F54)

ALLOCATION RESULT REGISTER

BIT

NAME

R/W

DESCRIPTION

FAILED

[6:5]

Reserved

[4:0]

P[4:0]

Returns Packet Number (0-31, 0x00-0x1F) from an allocation

command. This can be written directly into the PNR register

Table 84 - Packet Number Register

PNR (0x7F55)

PACKET NUMBER REGISTER

BIT

NAME

R/W

DESCRIPTION

[7:5

Reserved

[4:0]

P[4:0]

R/W

Packet selector to access packet at 0x6000 buffer window

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