Introduce Affine Controller Design

[ShangkunLi]

Add Affine Controller (AC) for Outer Loop Management

Summary

This PR introduces the Affine Controller (AC), a programmable hardware module that manages outer loop counters in the CGRA. While the existing LoopCounterRTL (DCU) handles innermost loop counting at the tile level, the AC coordinates multi-level loop nesting and cross-CGRA loop synchronization.

Architecture

The AC contains an array of Configurable Counter Units (CCUs), each representing one level of a loop nest. CCUs form a DAG topology where:

• Root CCUs drive the outermost loop with no parent
• Regular CCUs have a local parent CCU and report completion upward

Each CCU tracks a loop variable (lower_bound, upper_bound, step, current_value) and manages a set of targets — tile-array DCUs it must notify when advancing iterations.

State Machine: IDLE → RUNNING → DISPATCHING → RUNNING / COMPLETE

• RUNNING: Waiting for child completion events
• DISPATCHING: Sending commands to targets (1 cycle per target)
• COMPLETE: Loop finished, parent notified internally

Key Design Decisions

• Single-phase dispatch: Each target receives exactly one command per dispatch — either CMD_RESET_LEAF_COUNTER (leaf-mode DCU) or CMD_UPDATE_COUNTER_SHADOW_VALUE (delivery-mode DCU). This avoids redundant messages and minimizes dispatch latency.
• Internal CCU→parent completion: When a child CCU completes, it directly increments its parent's received_complete_count in the same cycle — no external signaling needed.
• Automatic child reset: When a parent CCU finishes dispatching and returns to RUNNING, all child CCUs are automatically reset to lower_bound.
• Last-iteration optimization: When current_value >= upper_bound, the CCU transitions directly to COMPLETE without dispatching, preventing stale completion events from the previous iteration.
• Backpressure on events: Both tile and remote completion events are only consumed when a matching CCU is in RUNNING state.

Cross-CGRA Support

CCU targets can be marked as remote (is_remote=1). Dispatch commands for remote targets are sent via send_to_remote (routed through the Controller's inter-CGRA NoC). Remote completion events arrive as CMD_AC_CHILD_COMPLETE on recv_from_remote.

Files Changed

File	Change
controller/AffineControllerRTL.py	[NEW] AC implementation (~400 lines)
controller/test/AffineControllerRTL_test.py	[NEW] 4 test cases
lib/cmd_type.py	Added 11 new AC command types, NUM_CMDS 28→40

Test Cases

Test	Description
test_basic_2_layer_loop	1 root CCU, 1 leaf DCU. Verifies basic dispatch and completion.
test_sibling_barrier	1 root CCU, 2 leaf DCUs (child_count=2). Verifies barrier synchronization.
test_3_layer_loop	CCU[0]→CCU[1]→DCU chain. Verifies internal CCU completion, parent dispatch, and child reset across 2×3=6 inner iterations.
test_cross_cgra_2_layer_loop	1 root CCU with remote + local targets. Verifies send_to_remote / recv_from_remote paths.

[tancheng]

How is the inner-loops start/end got updated?

[ShangkunLi]

How is the inner-loops start/end got updated?

Distributed counter units are updated through the cmds (including CMD_UPDATE_COUNTER_SHADOW_VALUE, CMD_RESET_LEAF_COUNTER)

[tancheng]

How is the inner-loops start/end got updated?

Distributed counter units are updated through the cmds (including CMD_UPDATE_COUNTER_SHADOW_VALUE, CMD_RESET_LEAF_COUNTER)

• What does "shadow" mean here?
• How do we make sure the inner-loops are already done with their execution before sending out the updated values/cmd?

[ShangkunLi]

How is the inner-loops start/end got updated?

Distributed counter units are updated through the cmds (including CMD_UPDATE_COUNTER_SHADOW_VALUE, CMD_RESET_LEAF_COUNTER)

• What does "shadow" mean here?

Shadow registers are used in the loop delivery mode in DCU to store and deliver the outer loop indexes.

VectorCGRA/fu/single/LoopCounterRTL.py

Line 134 in 61d7e56

s.send_out[0].msg @= s.shadow_regs[addr]

They are updated by the affine controller through the CMD_UPDATE_COUNTER_SHADOW_VALUE command.

VectorCGRA/fu/single/LoopCounterRTL.py

Line 150 in 61d7e56

elif s.recv_from_ctrl_mem.msg.cmd == CMD_UPDATE_COUNTER_SHADOW_VALUE:

• How do we make sure the inner-loops are already done with their execution before sending out the updated values/cmd?

Only DCUs in loop count mode will send a CMD_LEAF_COUNTER_COMPLETE command to the affine controller when it reaches the upper bound.

VectorCGRA/fu/single/LoopCounterRTL.py

Line 114 in 61d7e56

CMD_LEAF_COUNTER_COMPLETE, s.DataType(0, 0), 0, s.recv_opt.msg, addr

After receiving this complete signal, the affine controller will trigger outer loop counter increments and send CMD_UPDATE_COUNTER_SHADOW_VALUE & CMD_RESET_LEAF_COUNTER accordingly.