2.3.3. Upsizing data width function

The upsizer function can expand the data width by the following ratios:

Upsizing only packs write data for write or read transactions that are cacheable. This section describes the packing rules for different burst types and acceptance capabilities, and the following definitions apply:

Note

  • If the network splits input exclusive transactions into more than one output bus transaction, it removes the exclusive information from the multiple transactions it creates.

  • If multiple responses from created transactions are combined into one response, then the order of priority is:

    • DECERR is the highest priority.

    • SLVERR is the next highest priority.

    • OKAY is the lowest priority.

In the examples in this section, the input data width is 64 bits, and the output data width is 128 bits, unless otherwise stated. This section describes:

INCR bursts

The network converts all input INCR bursts that complete within a single output data width into an INCR1 of the minimum SIZE possible, and it packs all INCR bursts into INCR bursts of the optimum size possible. Table 2.4 shows how the network converts INCR bursts when it upsizes them.

Table 2.4. Conversion of INCR bursts by the upsizer function

INCR burst typeConverted to
64-bit INCR1Passes through unconverted
64-bit aligned INCR2INCR1
8-bit aligned INCR8INCR1, 64-bit
8-bit unaligned, byte address 1, 2, or 3, INCR5INCR1, 128-bit
8-bit unaligned, byte address 4, 5, 6, or 7, INCR5INCR2, 64-bit
64-bit unaligned INCR2Passes through unconverted
64-bit aligned INCR4INCR2
64-bit unaligned INCR4Sparse INCR3

Note

Bursts are never merged.

Upsize

When upsizing and protocol converting to or from AXI3 and AXI4, then the following maximum INCR burst lengths are shown in Table 2.5.

Table 2.5. Maximum INCR burst lengths

RatioAXI3 to AXI3AXI3 to AXI4AXI4 to AXI4AXI4 to AXI3
1:2Maximum Len16 outputMaximum Len16 outputMaximum Len256 outputMaximum Len16 output
1:4Maximum Len16 outputMaximum Len16 outputMaximum Len256 outputMaximum Len16 output
1:8Maximum Len16 outputMaximum Len16 outputMaximum Len256 outputMaximum Len16 output

WRAP bursts

All WRAP bursts are either passed through unconverted as WRAP bursts, or converted to one or two INCR bursts of the output bus. Table 2.6 shows how the network converts WRAP bursts when it upsizes them from 64 bits to 128 bits, that is, a ratio of 1:2.

Table 2.6. Conversion of WRAP bursts by the upsizer function

WRAP burst typeConverted to
128-bit aligned WRAP2INCR1.
128-bit aligned WRAP4WRAP2.
128-bit unaligned WRAP4

Depending on the address:

  • INCR2 + INCR1.

  • INCR1 + INCR2.


Note

The network converts input WRAP bursts with a total payload that is less than the output data width to a single INCR.

Fixed bursts

All FIXED bursts pass through unconverted.

Bypass merge

You can configure the upsizer function to have a programmable bit named bypass_merge. If bypass_merge is asserted, the network does not alter any transactions that can pass through legally without alteration.

Acceptance capability

You can configure the upsizer to support 1-32 read transactions and 1-32 write transactions. The issuing capability is a maximum of twice the acceptance capability.

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