Avalon® Interface Specifications

ID 683091
Date 9/26/2022
Document Table of Contents

3.7. Avalon® -MM Agent Addressing

Dynamic bus sizing manages data during transfers between host-agent pairs of differing data widths. Agent data are aligned in contiguous bytes in the host address space.

If the host data width is wider than the agent data width, words in the host address space map to multiple locations in the agent address space. For example, a 32-bit host read from a 16-bit agent results in two read transfers on the agent side. The reads are to consecutive addresses.

If the host is narrower than the agent, then the interconnect manages the agent byte lanes. During host read transfers, the interconnect presents only the appropriate byte lanes of agent data to the narrower host. During host write transfers, the interconnect automatically asserts the byteenable signals to write data only to the specified agent byte lanes.

Agents must have a data width of 8, 16, 32, 64, 128, 256, 512 or 1024 bits. The following table shows the alignment for agent data of various widths within a 32-bit host performing full-word accesses. In this table, OFFSET[N] refers to a agent word size offset into the agent address space.

Table 12.  Dynamic Bus Sizing Host-to-Agent Address Mapping
Host Byte Address  (1) Access 32-Bit Host Data
When Accessing 
an 8-Bit Agent Interface When Accessing 
a 16-Bit Agent Interface When Accessing 
a 64-Bit Agent Interface
0x00 1 OFFSET[0] 7..0 OFFSET[0] 15..0  (2) OFFSET[0] 31..0
2 OFFSET[1] 7..0 OFFSET[1] 15..0
3 OFFSET[2] 7..0
4 OFFSET[3] 7..0
0x04 1 OFFSET[4] 7..0 OFFSET[2] 15..0 OFFSET[0] 63..32
2 OFFSET[5] 7..0 OFFSET[3] 15..0
3 OFFSET[6] 7..0
4 OFFSET[7] 7..0
0x08 1 OFFSET[8] 7..0 OFFSET[4] 15..0 OFFSET[1] 31..0
2 OFFSET[9] 7..0 OFFSET[5] 15..0
3 OFFSET[10] 7..0
4 OFFSET[11] 7..0
0x0C 1 OFFSET[12] 7..0 OFFSET[6] 15..0 OFFSET[1] 63..32
2 OFFSET[13] 7..0 OFFSET[7] 15..0
3 OFFSET[14] 7..0
4 OFFSET[15] 7..0
And so on   And so on And so on And so on
  1. Although the host issues byte addresses, the host accesses full 32-bit words.
  2. For all agent entries, [<n>] is the word offset and the subscript values are the bits in the word.