LAN91C100FD datasheet(49/79 Pages) SMSC

49 / 79 page

FEAST Fast Ethernet Controller with Full Duplex Capability

SMSC DS – LAN91C100FD Rev. D

Page 49

Rev. 10/14/2002

PRELIMINARY

Figure 5.7 - Drive Send and Allocate Routines

5.5

Memory Partitioning

Unlike other controllers, the LAN91C100FD does not require a fixed memory partitioning between transmit

and receive resources. The MMU allocates and de-allocates memory upon different events. An additional

mechanism allows the CPU to prevent the receive process from starving the transmit memory allocation.

ALLOCATE

Issue "Allocate Memory"

Command to MMU

Read Interrupt Status Register

Enqueue Packet

Set "Ready for Packet" Flag

Return

Copy Remaining TX Data

Packet into RAM

Return Buffers to Upper Layer

Write Allocated Packet into

Packet # Register

Write Address Pointer Register

Copy Part of TX Data Packet

into RAM

Write Source Address into

Proper Location

Store Data Buffer Pointer

Clear "Ready for Packet" Flag

Enable Allocation Interrupt

Allocation

Passed?

Yes

DRIVER SEND

Choose Bank Select

Call ALLOCATE

Exit Driver Send

Read Allocation Result

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