AVL-AXI Item

Due to the inherent independence of reads and writes the SequenceItem is split into WriteItem and ReadItem.

All System parameters are inherited from the interface but marked as “hidden” (prefixed and suffixed with “_”). This provides the full context for any additional functionality to be implemented without additional hook. (e.g. custom checks or coverage).

Only payload signals are included in the items. Protocol signals such as valid and ready are explicitly driven and observed buy the drivers and monitors respectively.

Due to the number of sidebands and combinations of parameters, the item variables are assigned in loops defined in avl_axi._signals.

Items string formats are transposed by default to make the display more human readable:

+-----------+------+--------+-------+--------+---------+-------------+--------------------+-------+-----+----------------+-------+-----+-------+----------------+---------------+---------------+
| name      | awid | awaddr | awlen | awsize | awburst | awatop      | wdata              | wstrb | rid | rdata          | rresp | bid | bresp | aw_wait_cycles | w_wait_cycles | b_wait_cycles |
+-----------+------+--------+-------+--------+---------+-------------+--------------------+-------+-----+----------------+-------+-----+-------+----------------+---------------+---------------+
| from_mseq | 0x1  | 0x1000 | 0x0   | 0x3    | FIXED   | LOAD_LE_CLR | 0xffff00000000ffff | 0x0   | 0x1 | 0xffffffffffff | OKAY  | 0x1 | OKAY  | 0              | 0             | 0             |
+-----------+------+--------+-------+--------+---------+-------------+--------------------+-------+-----+----------------+-------+-----+-------+----------------+---------------+---------------+


+-----------+------+--------+-------+--------+---------+-------------+-------+-------+-----+--------+-------+-----+-------+----------------+---------------+---------------+
| name      | awid | awaddr | awlen | awsize | awburst | awatop      | wdata | wstrb | rid | rdata  | rresp | bid | bresp | aw_wait_cycles | w_wait_cycles | b_wait_cycles |
+-----------+------+--------+-------+--------+---------+-------------+-------+-------+-----+--------+-------+-----+-------+----------------+---------------+---------------+
| from_mseq | 0x3  | 0x1000 | 0x7   | 0x3    | INCR    | LOAD_LE_SET | 0x1   | 0x0   | 0x3 | 0xaa00 | OKAY  | 0x3 | OKAY  | 0              | 0             | 0             |
|           |      |        |       |        |         |             | 0x2   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x3   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x4   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x5   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x6   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x7   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
|           |      |        |       |        |         |             | 0x8   | 0x0   | 0x3 | 0xaa00 | OKAY  |     |       |                | 0             |               |
+-----------+------+--------+-------+--------+---------+-------------+-------+-------+-----+--------+-------+-----+-------+----------------+---------------+---------------+

Set / Get Functions

Due to the configurable nature of the interface the user should use the SequenceItem.set and SequenceItem.get functions. These handle access to the underlying value while safely ignoring / providing defaults for missing fields. This allows the user to safely code generic functions without having to constantly check the parameters of the given interface.

Enumerations

AVL ENUMs are not used for the enumerated types in AVL-AXI. This is due to the configurability of the width in many cases. Certain parameters add additional values to a given enum. As such enums in avl_axi._types are implemented as Logic variables with custom fmt and values functions. Class variables are also present to make for easy export.

By default the most complete enum is the default, but fields are removed by width constraints.

Randomization

Where possible AVL Z3 are added to the enum avl_axi._types and SequenceItem to ensure legal values are generated.

Any enum value marked as “RESERVED” should be excluded in randomization by default, however these constraints can be removed using the remove_constraint function in the item or variable.

Resize

By default items contain defaultdicts for all W and R payloads. A SequenceItem.resize function is provided to pad any remaining data based on awlen / arlen.This function is called automatically in the SequenceItem.post_randomize function or by the sequence when directed stimulus is used.

defaultdicts have been used for performance. The overhead of creating the 256 beats worth of data is high. The monitors naturally populate all beats with the correct payloads. This is checked using the SequenceItem.sanity function, called before the monitor exports the item. SequenceItem.resize is called as part of the sequence to fully populate the remaining data in both the randomized and directed sequences.

The downside is that the data contained in the W and R phases are now dicts / arrays indexed by position. However, the ManagerSequence.write and ManagerSequence.read functions allow these to be defined as dicts or lists for the users convenience.

Comparison functions remain unchanged.

Should the user which to limit the number of beats in a transaction, standard constraints are usable:

# Constraint Writes
self.add_constraint("c_custom_write", lambda x : ULE(x, 8), self.awlen)

# Constrain Reads
self.add_constraint("c_custom_read", lambda x : ULE(x, 8), self.arlen)

Sanity

A SequenceItem.sanity function is provided to ensure and intra item constraints are kept. For example arid and rid must match within a single item. This function is called by the WriteMonitor and ReadMonitor when the transaction response phase is completed.

Regular Transactions Only

One possible configuration option is to limit the AXI bus to issue only regular transactions. This is a limited range of lengths, sizes and burst types.

The SequenceItem supports this function using both constraints and the SequenceItem.post_randomize function. Address alignment is handled in SequenceItem.post_randomize for simplicity and performance consideration

Fixed Burst Disable

Another possible configuration prevents ths AXI bus issuing FIXED burst types. This is handled automatically with constraints and sanity checks.

Max Transaction Bytes

All AXI interfaces have a maximum number of transaction bytes. This defaults to 4096. This is handled automatically with constraints and sanity checks.