Diagonal Processing Element (pe_diag.sv)

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Source file: rtl/systolic_gauss_jordan/pe_diag.sv

Elementary Processing element used across the systolic mesh Trapezoidal mesh (trapeziod_mesh.sv) which processes diagonal elements of incoming columns (pivots of each row). The opcode (op_o/op_i) enums are defined in Shared package (gj_pkg.sv)

Ports

Inputs

• clk: clock signal

• rst: reset

• en_i: enable

• data_i: data bit in

• reduce_sig_i: reduce signal activating reduction for the pivot column.

Outputs

• data_o: data bit out

• op_o: opcode out

• reduce_sig_o: reduce signal activating reduction for the pivot column.

Behaviour

• During the forward pass: drives the rightward movement of opcode which signals weather a pivot element has been found

• Drives the downward data output seen by the next row

• During the reduce pass: forwards a delayed diagonal reduce signal

Transition table

Notes:

• r is the current stored bit.

• r_next is the next stored bit.

• data_out_next is the combinational value later registered into data_o.

• op_out_next is the combinational value later registered into op_o.

• state_o is always the registered state bit r.

Reduce signal forwarding

rst	reduce_sig_i	reduce_sig_o	Meaning
1	x	0	Mask reduce during reset
0	reduce_sig_i	reduce_sig_i	Forward reduce unchanged

Enabled data path (rst = 0, en_i = 1)

reduce_sig_i	data_i	r	r_next	data_out_next	op_o after clock	Meaning
1	data_i	1	1	data_i	OP_SWAP	Active reduce branch
0 or 1	0	r	r	0	OP_PASS	Zero input keeps state and drives zero downward
0 or 1	1	0	1	0	OP_LOCK	First 1 locks the diagonal state
0	1	1	1	0	OP_ADD	Forward-mode add branch after the pivot is already locked

Notes:

• op_o after clock is the registered copy of op_out_next.

• data_out_next defaults to 1'b0 before the branch logic and is only overridden in the active reduce branch.

Test

• Test file: test_pe_diag.py

make -C test/systolic_gauss_jordan TEST=pe_diag