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Added JTAG interface with testbench

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This commit is contained in:
Joppe Blondel
2026-02-23 15:37:49 +01:00
parent 20cfece6e3
commit 8f4e887b9d
12 changed files with 731 additions and 24 deletions
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25
sim/other/test.svf Normal file
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TRST ABSENT;
ENDIR IDLE;
ENDDR IDLE;
STATE RESET;
STATE IDLE;
SIR 6 TDI (02);
SDR 8 TDI (07);
SDR 8 TDI (4C);
SDR 8 TDI (43);
SDR 8 TDI (D1);
SDR 8 TDI (97);
SDR 8 TDI (6B);
SDR 8 TDI (3D);
SDR 8 TDI (E4);
SDR 8 TDI (20);
SDR 8 TDI (3A);
SDR 8 TDI (8E);
SDR 8 TDI (1D);
SDR 8 TDI (9D);
SDR 8 TDI (E4);
RUNTEST 16 TCK;
STATE RESET;
STATE IDLE;

196
sim/overrides/jtag_if.v Normal file
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`timescale 1ns/1ps
// =============================================================================
// JTAG interface (simulation override)
// Behavioral SVF player for simple USER-chain simulation.
//
// Supported SVF commands (line-oriented, uppercase recommended):
// - SIR <n> TDI (<hex>);
// - SDR <n> TDI (<hex>);
// - RUNTEST <n> TCK;
// - STATE RESET;
// - STATE IDLE;
// Other lines are ignored.
// =============================================================================
module jtag_if #(
parameter integer chain = 1,
parameter [8*256-1:0] SVF_FILE = "write_jtag.svf",
parameter integer TCK_HALF_PERIOD_NS = 50,
parameter [31:0] USER_IR_OPCODE = 32'h00000002
)(
input wire i_tdo,
output reg o_tck,
output reg o_tdi,
output reg o_drck,
output reg o_capture,
output reg o_shift,
output reg o_update,
output reg o_runtest,
output reg o_reset,
output reg o_sel
);
integer fd;
integer got;
integer nbits;
integer cycles;
integer i;
integer line_no;
integer scan_bits;
reg [8*1024-1:0] line;
reg [8*32-1:0] cmd;
reg [8*32-1:0] arg1;
reg [8*256-1:0] svf_file_path;
reg [4095:0] scan_data;
reg [31:0] current_ir;
reg selected;
// Keep linters quiet: TDO is not consumed by this simple player.
wire _unused_tdo;
assign _unused_tdo = i_tdo;
task pulse_tck;
begin
#TCK_HALF_PERIOD_NS o_tck = 1'b1;
#TCK_HALF_PERIOD_NS o_tck = 1'b0;
end
endtask
task pulse_drck_shift;
input bit_in;
begin
o_tdi = bit_in;
o_shift = 1'b1;
#TCK_HALF_PERIOD_NS begin
o_tck = 1'b1;
o_drck = 1'b1;
end
#TCK_HALF_PERIOD_NS begin
o_tck = 1'b0;
o_drck = 1'b0;
end
end
endtask
task pulse_capture;
begin
o_capture = 1'b1;
#TCK_HALF_PERIOD_NS begin
o_tck = 1'b1;
o_drck = 1'b1;
end
#TCK_HALF_PERIOD_NS begin
o_tck = 1'b0;
o_drck = 1'b0;
o_capture = 1'b0;
end
end
endtask
task pulse_update;
begin
o_shift = 1'b0;
#TCK_HALF_PERIOD_NS o_update = 1'b1;
#TCK_HALF_PERIOD_NS o_update = 1'b0;
end
endtask
initial begin
// Default output levels
o_tck = 1'b0;
o_tdi = 1'b0;
o_drck = 1'b0;
o_capture = 1'b0;
o_shift = 1'b0;
o_update = 1'b0;
o_runtest = 1'b0;
o_reset = 1'b0;
o_sel = 1'b0;
selected = 1'b0;
current_ir = 32'h0;
line_no = 0;
svf_file_path = SVF_FILE;
// Deterministic startup reset pulse before consuming SVF.
o_reset = 1'b1;
#TCK_HALF_PERIOD_NS o_tck = 1'b1;
#TCK_HALF_PERIOD_NS o_tck = 1'b0;
#TCK_HALF_PERIOD_NS o_tck = 1'b1;
#TCK_HALF_PERIOD_NS o_tck = 1'b0;
o_reset = 1'b0;
fd = $fopen(svf_file_path, "r");
if (fd == 0) begin
$display("jtag_if(sim): could not open SVF file '%0s'", svf_file_path);
end else begin
while (!$feof(fd)) begin
line = {8*1024{1'b0}};
got = $fgets(line, fd);
line_no = line_no + 1;
if (got > 0) begin
cmd = {8*32{1'b0}};
arg1 = {8*32{1'b0}};
scan_data = {4096{1'b0}};
nbits = 0;
cycles = 0;
got = $sscanf(line, "%s", cmd);
if (got < 1) begin
// Empty line
end else if (cmd == "!") begin
// Comment line
end else if (cmd == "SIR") begin
got = $sscanf(line, "SIR %d TDI (%h);", nbits, scan_data);
if (got == 2) begin
current_ir = scan_data[31:0];
selected = (current_ir == USER_IR_OPCODE);
o_sel = selected;
// Emit TCK pulses for IR shift activity.
scan_bits = nbits;
if (scan_bits > 4096) scan_bits = 4096;
for (i = 0; i < scan_bits; i = i + 1) begin
o_tdi = scan_data[i];
pulse_tck;
end
end
end else if (cmd == "SDR") begin
got = $sscanf(line, "SDR %d TDI (%h);", nbits, scan_data);
if (got == 2) begin
if (selected) begin
pulse_capture;
end
scan_bits = nbits;
if (scan_bits > 4096) scan_bits = 4096;
for (i = 0; i < scan_bits; i = i + 1) begin
pulse_drck_shift(scan_data[i]);
end
if (selected) begin
pulse_update;
end
end
end else if (cmd == "RUNTEST") begin
got = $sscanf(line, "RUNTEST %d TCK;", cycles);
if (got == 1) begin
o_runtest = 1'b1;
for (i = 0; i < cycles; i = i + 1)
pulse_tck;
o_runtest = 1'b0;
end
end else if (cmd == "STATE") begin
got = $sscanf(line, "STATE %s", arg1);
if (got == 1) begin
if (arg1 == "RESET;") begin
o_reset = 1'b1;
#TCK_HALF_PERIOD_NS o_reset = 1'b0;
selected = 1'b0;
o_sel = 1'b0;
end
end
end
end
end
$fclose(fd);
end
end
endmodule

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sim/tb/tb_svf.v Normal file
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`timescale 1ns/1ps
module tb_svf();
wire [7:0] led_out;
wire [31:0] update_count;
jtag_byte_sink #(
.SVF_FILE("sim/other/test.svf"),
.TCK_HALF_PERIOD_NS(50)
) dut (
.o_led(led_out),
.o_update_count(update_count)
);
initial begin
// Optional waveform dump.
$dumpfile("out.vcd");
$dumpvars;
// Timeout for large SVF playback.
#20_000;
$finish;
end
endmodule
module jtag_byte_sink #(
parameter [8*256-1:0] SVF_FILE = "",
parameter integer TCK_HALF_PERIOD_NS = 50
)(
output reg [7:0] o_led,
output reg [31:0] o_update_count
);
wire jtag_tck;
wire jtag_tdi;
wire jtag_drck;
wire jtag_capture;
wire jtag_shift;
wire jtag_update;
wire jtag_runtest;
wire jtag_reset;
wire jtag_sel;
wire jtag_tdo;
reg [7:0] shift_reg;
assign jtag_tdo = shift_reg[0];
jtag_if #(
.chain(1),
.SVF_FILE(SVF_FILE),
.TCK_HALF_PERIOD_NS(TCK_HALF_PERIOD_NS),
.USER_IR_OPCODE(32'h0000_0002)
) jtag (
.i_tdo(jtag_tdo),
.o_tck(jtag_tck),
.o_tdi(jtag_tdi),
.o_drck(jtag_drck),
.o_capture(jtag_capture),
.o_shift(jtag_shift),
.o_update(jtag_update),
.o_runtest(jtag_runtest),
.o_reset(jtag_reset),
.o_sel(jtag_sel)
);
always @(posedge jtag_drck or posedge jtag_reset) begin
if (jtag_reset) begin
shift_reg <= 8'h00;
end else if (jtag_sel && jtag_capture) begin
shift_reg <= o_led;
end else if (jtag_sel && jtag_shift) begin
shift_reg <= {jtag_tdi, shift_reg[7:1]};
end
end
always @(posedge jtag_update or posedge jtag_reset) begin
if (jtag_reset) begin
o_led <= 8'h00;
o_update_count <= 32'd0;
end else if (jtag_sel) begin
o_led <= shift_reg;
o_update_count <= o_update_count + 1'b1;
end
end
// Keep lint happy for currently unused outputs.
wire _unused_tck;
wire _unused_runtest;
assign _unused_tck = jtag_tck;
assign _unused_runtest = jtag_runtest;
endmodule