Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R Receive Side Scaling (BCM5755 and BCM5755M Only) Page 72
Figure 29: RSS Receive Processing Sequence
The BCM5755 and BCM5755M devices implement the above RSS algorithm in hardware except for the step of adding the
Base CPU Number to the value from Indirection Table. If required, the step of adding the Base CPU Number to the CPU
Result can be done in the main Interrupt Service Routine to determine which CPU will process the packet.
RSS PARAMETERS
Hash Function
The default hash function is the Toeplitz hash. No other hash functions are currently supported. So there is no configurable
parameter.
Hash Type
The fields that are used to hash across the incoming packet. The BCM5755 and BCM5755 devices support all the four hash
types given below and the configuration bits for enabling/disabling these hash types are provided in Receive MAC Mode
register at offset 0x468. Any combination of these hash types can be enabled:
• Four-tuple of source TCP Port, source IP version 4 (IPv4) address, destination TCP port, and destination IPv4 address.
• Four-tuple of source TCP Port, source IP version 6 (IPv6) address, destination TCP port, and destination IPv6 address.
• Two-tuple of source IPv4 address and destination IPv4 address.
• Two-tuple of source IPv6 address and destination IPv6 address.
Hash Mask
The RSS Hash Mask bits (bits 22:20 of the Receive MAC Mode register at offset 0x468) allow the configuration of number
of hash-result bits that are used to index into the indirection table.
Indirection Table
The table of CPU numbers used for balancing the receive traffic across multiple processors. The Indirection Table registers
0–15 at offset 0x630–0x66F are implemented for the required 128 entries of the Indirection Table. The BCM5755 and
BCM5755M support only four Receive Return Rings so each entry of Indirection Table is implemented as 2 bits.
Hash
Function
Incoming Packe
Hash Result
(32 Bits)
CPU
Result
Indirection
Table
Hash
Mask
Masked
Hash Result
1-7 Bits
32-Bit Hash Result
Hash Type
+
Base CPU Number
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