AXI4 VIP development and integration by tchilikov-semify · Pull Request #688 · lowRISC/mocha

tchilikov-semify · 2026-07-22T11:29:50Z

This PR does a few things:

Pulls @rswarbrick's AXI driver from his Caliptra repository as a local copy and expands on its functionality with multi-beat support
Merges it with Csaba's AXI monitor from Axi4 passive vip #391, creating one unified agent for Active (manager) and Passive (monitor) modes
Applies various bug and compilation fixes to the agent
Integrates the agent in the top TB as a monitor on each port of the crossbar
creates an environment level scoreboard

This was tested with the top level CVA6-based test cases.

Will close issue #168

rswarbrick

Thank you very much for doing this (and getting my completely untested code working...)

Do you think you could cherry-pick the various fixes in "axi agent compilation fixes" to the commits that made the mistakes? Since we don't use squash merge in Mocha, this is a way to avoid putting Rupert's silly mistakes into the history :-)

tchilikov-semify · 2026-07-22T13:11:04Z

Thank you very much for doing this (and getting my completely untested code working...)

Do you think you could cherry-pick the various fixes in "axi agent compilation fixes" to the commits that made the mistakes? Since we don't use squash merge in Mocha, this is a way to avoid putting Rupert's silly mistakes into the history :-)

Hey Rupert,

Sure, I can merge the patches into your commits. This would also encompass the handshaking bugfix commit, for a total of two commits :)

This is the first step towards a simple AXI agent. It will only have to handle the subset of AXI that is in use in the blocks in question (which work by translating to TLUL, so they aren't doing anything particularly exciting). In this commit, we're just defining interfaces for the five channels (which are AW, W, B, AR and R). Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

The axi_read_request_item and axi_read_data_item classes are intended to be randomised (when a sequence wishes to send either read requests or data responses). The axi_read_item class can be used by a monitor that sees a read request and then one or more responses. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

When the agent is representing an AXI Manager, this will be useful for the B and R channels. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

These drive write requests (AW) and write data (W) and also drive the write response channel (B). Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

For an example use-case, suppose you are reading with AR / R transfers. You send an AR transfer with some ARID that will have a burst with k beats. Now you want consume read data with that many (k) R transfers using the some ID. To do so: - Run k axi_mgr_read_data_seq sequences, calling on_response() after each finishes. - (In parallel) call wait_for_response() k times. The trick is that these sequences might respond with different IDs, but that doesn't matter: the sequences are just actings as tokens to allow *something* to come back.

rswarbrick · 2026-07-22T13:17:42Z

+  extern function new(string name = "axi_agent_cfg");
+
+  // Set the identity/policy/width fields in one call. The interfaces are set separately by the BFM.
+  extern function void set_config(string                  inst_id         = "axi_mgr",


I'm really not a fan of big lines of arguments with default values. As I wrote above, I think you only need to set is_active and enable_coverage. I'd suggest forcing the caller to pass both.

rswarbrick · 2026-07-22T13:19:32Z

  super.build_phase(phase);

-  if (m_cfg == null && !uvm_config_db#(axi_agent_cfg)::get(this, "", "cfg", m_cfg)) begin
+  if (m_cfg == null && !uvm_config_db#(axi_agent_cfg)::get(this, "", "axi_agent_cfg", m_cfg)) begin


Ooh: I'm not a fan of this. You'll end up with a path that looks like "my_env.m_axi_agent.axi_agent_cfg". What's wrong with "my_env.m_axi_agent.cfg"?

rswarbrick · 2026-07-22T13:43:49Z

+// Merged-transaction item from axi_monitor: holds a whole write (AW + W beats +
+// B) or a whole read (AR + R beats); obs_kind says which. Per-beat W/R payloads
+// are queues. Field widths mirror the per-channel axi_*_if max footprint.


I'm not a huge fan of this: it feels extremely "untyped": the way one has to encode sum types in C++...

I'd much rather have several different types, maybe

axi_mon_write (AW + a queue of W x B pairs)

axi_mon_read (AR + a queue of R items)

Would something like that work? I think it might be more pleasant for whatever lies "downstream".

tchilikov-semify · 2026-07-22T14:15:10Z

Hey @rswarbrick,
Thanks a lot for the in-depth review! I'll go through all of the comments and address them.

In the meanwhile, I've folded the old compilation bugfixes commit into the respective commits that you made, so the commit history should be clear of bugs now.

This is a bare-bones agent for the five AXI interfaces. Note that there are no monitors, so the agent won't actually do anything in passive mode (yet). Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

To make it easier to "write address 123", there is an easy way to constrain the (single) sequence item in the sequence. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

The general sequence is axi_mgr_write_data_seq, but there is also a specialisation that sends exactly one transfer. This makes it easier to randomise a degenerate, length-one burst. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

To do so, we add a (pretty trivial) reg_adapter and a sequencer in a layered vseq that runs the resulting translated items. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

tchilikov-semify requested review from marnovandermaas, martin-velay and rswarbrick July 22, 2026 11:29

tchilikov-semify mentioned this pull request Jul 22, 2026

Axi4 passive vip #391

Closed

tchilikov-semify requested a review from thommythomaso July 22, 2026 11:38

tchilikov-semify force-pushed the axi_driver_pr_new branch 3 times, most recently from 01fb3d1 to 3863316 Compare July 22, 2026 12:23

rswarbrick reviewed Jul 22, 2026

View reviewed changes

rswarbrick and others added 8 commits July 22, 2026 14:40

[dv,axi] Implement items for AXI write transactions

b59c688

[dv,axi] Define an item type to control how we accept responses

76a5434

When the agent is representing an AXI Manager, this will be useful for the B and R channels. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Implement drivers for the Manager side of write channels

0ab815d

These drive write requests (AW) and write data (W) and also drive the write response channel (B). Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Implement drivers for the Manager side of read channels

eeea7ec

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Define item and monitor for resets on each AXI interface

8676709

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

rswarbrick reviewed Jul 22, 2026

View reviewed changes

tchilikov-semify force-pushed the axi_driver_pr_new branch from 3863316 to 0d44df6 Compare July 22, 2026 14:10

tchilikov-semify force-pushed the axi_driver_pr_new branch 4 times, most recently from 8f7d14d to 42c6a8d Compare July 22, 2026 15:09

rswarbrick and others added 5 commits July 22, 2026 16:23

[dv,axi] Define axi_mgr_agent

e078470

This is a bare-bones agent for the five AXI interfaces. Note that there are no monitors, so the agent won't actually do anything in passive mode (yet). Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Define a sequence with a single read or write request

270499c

To make it easier to "write address 123", there is an easy way to constrain the (single) sequence item in the sequence. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Define a sequence to consume the AXI write response

ebca3b5

[dv,axi] Define a sequence to consume AXI read data

c161b61

rswarbrick and others added 9 commits July 22, 2026 16:23

[dv,axi] A virtual sequence that does a single write transfer

5df0054

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] A virtual sequence that does a single read transfer

fa138f2

Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] Allow axi_agent to connect to the register layer

525ed3e

To do so, we add a (pretty trivial) reg_adapter and a sequencer in a layered vseq that runs the resulting translated items. Co-authored-by: tchilikov-semify <christian.tchilikov@semify-eda.com>

[dv,axi] fix axi handshaking for beat sampling on multi-beat traffic

216931e

[dv,axi] add multi-beat transaction support to driver

9d09cad

[dv,axi] add clk_rst_if to axi interfaces

dcbe94d

[dv,axi] add a passive monitor to AXI agent

d095438

[dv,axi] add axi_vip wrapper to agent

fffddb2

[dv,top] integrate AXI4 monitors in top tb

bbc5a9c

tchilikov-semify force-pushed the axi_driver_pr_new branch from 42c6a8d to bbc5a9c Compare July 22, 2026 15:27

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AXI4 VIP development and integration#688

AXI4 VIP development and integration#688
tchilikov-semify wants to merge 22 commits into
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