Buffer Manager RegistersBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 430
MBUF Pool Length Register (offset: 0x440C)
The register specifies the length of MBUF.
Read DMA MBUF Low Watermark Register (offset: 0x4410)
This 6-bit register indicates the number of free MBUFs that must be available for the Read DMA Engine to
dequeue a descriptor from the normal priority FTQ. If the free MBUF count drops below this mark, it must go
above the high watermark to resume normal operation.
MAC RX MBUF Low Watermark Register (offset: 0x4414)
This 9-bit register indicates the number of free MBUFs that must be available for the RX MAC to accept a frame.
If the free MBUF count drops below this mark, it must go above the high watermark to resume normal operation.
Read DMA MBUF High Watermark Register (offset: 0x4418)
This 9-bit register indicates the number of free MBUFs that must be available before normal operation is
restored to the Read DMA Engine and/or the RX MAC.
RX RISC MBUF Cluster Allocation Request Register (offset: 0x441C)
The RX RISC MBUF Cluster Allocation Request register contains two fields:
• A requested size field which can be up to 64 KB long
• An allocation bit
The allocation bit is used to control the access to the response register. Use this register to set the size and
allocation bit and then poll the register until the allocation bit is cleared. When the allocation bit is cleared, it is
safe to read from the RX RISC MBUF Cluster Allocation Response register.
Name Bits Access
Default
Value
Description
Reserved 31:23 RO 0 –
MBUF Length 22:0 RW 0xA000h Specifies the length of MBUF assigned for
receive packet. The default is 32 KB. The lower
seven bits should be ignored to align the MBUF
pool on a 128-byte boundary.
Name Bits Access
Default
Value
Description
Allocation Bit 31 RW 0 Set this bit to 1 to request for the MBUF.
When this bit is read as 0, then read the MBUF
allocation Response register for the TXMBUF
pointer.
Reserved 30:0 RO 0 –
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