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Add SPI testbench

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Jeremy Shen
2026-06-08 10:14:17 +08:00
parent 4fd22c4919
commit 61076299a0
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CPLD1/tb_SPI_RegRW_formal.sv
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//------------------------------------------------------------------------------
//
// Testbench: CPLD1 - SPI Formal Verification
// Project: NewCalBoard DIG
// Tool: Lattice Diamond Verilog-2001 / QuestaSim (Lattice OEM)
// Purpose: Formal verification of SPI protocol using explicit checks
//
// Interface: 4 wires only (i_sclk, i_cs, i_mosi, o_miso)
//
// Protocol:
// Write: [1][Addr:7b][Data:24b] = 32 bits
// Read: [0][Addr:7b][Don'tCare:24b] -> MISO returns [8'h00][24-bit rdata]
//
// Properties Verified (Explicit Checks):
// P1: Frame structure - 32-bit transfer on CS assertion
// P2: Write frame format - MSB first, write bit = 1
// P3: Read frame format - MSB first, read bit = 0
// P4: MISO response on read - 8'h00 prefix + 24-bit rdata
// P5: CS alignment - transfer completes within one CS low window
// P6: Register write persistence - written value survives subsequent reads
// P7: IDENT register read-only - always returns 24'h200110
// P8: MISO shift timing - data shifts out on falling edge (Mode 0)
// P9: No spurious MISO transitions during CS high
// P10: Sequential transfers - independent frame boundaries
// P11: Boundary conditions - min/max/alternate bit patterns
//
//------------------------------------------------------------------------------
`timescale 1ns / 1ps
`define SYS_CLK_PERIOD 20 // 50 MHz system clock
`define SPI_CLK_PERIOD 400 // 1 MHz SPI clock
`define BITS_PER_FRAME 32
module tb_SPI_RegRW_formal;
//==========================================================================
// Clock & Reset
//==========================================================================
reg i_sys_clk;
reg i_rst_n;
// SPI interface - exactly 4 wires, matching real hardware
reg i_sclk;
reg i_cs;
reg i_mosi;
wire o_miso;
// Clock generation
initial begin
i_sys_clk = 0;
forever #(`SYS_CLK_PERIOD / 2) i_sys_clk = ~i_sys_clk;
end
initial begin
i_sclk = 0;
forever #(`SPI_CLK_PERIOD / 2) i_sclk = ~i_sclk;
end
//==========================================================================
// DUT instantiation - 4 SPI wires only
//==========================================================================
RelayConTop DUT (
.i_sys_clk(i_sys_clk),
.i_rst_n (i_rst_n),
.i_sclk (i_sclk),
.i_mosi (i_mosi),
.i_cs (i_cs),
.o_miso (o_miso)
);
//==========================================================================
// Internal signals for formal verification
//==========================================================================
reg [31:0] formal_cmd; // Command being sent
reg [31:0] formal_rdata; // Captured response
reg formal_pass; // Overall pass flag
reg formal_fail; // Overall fail flag
integer formal_fail_count;
integer formal_pass_count;
integer formal_total_count;
integer bit_idx;
//==========================================================================
// Formal Stimulus Generator Tasks
//==========================================================================
// Generate a 32-bit frame on the SPI bus
// Mode 0 (CPOL=0, CPHA=0): MSB first, data setup on falling edge
task formal_send_frame;
input [31:0] cmd;
begin
formal_cmd = cmd;
// Wait for a stable point, then assert CS
@(negedge i_sclk);
i_cs = 1'b0;
i_mosi = cmd[31];
// Shift out 32 bits MSB first
for (bit_idx = 31; bit_idx >= 0; bit_idx = bit_idx - 1) begin
@(posedge i_sclk); // DUT samples MOSI on rising edge
if (bit_idx > 0) begin
@(negedge i_sclk); // Setup next bit on falling edge
i_mosi = cmd[bit_idx - 1];
end
end
// Deassert CS
@(negedge i_sclk);
i_cs = 1'b1;
i_mosi = 1'b0;
@(negedge i_sclk);
end
endtask
// Generate a 32-bit frame and capture MISO response
// Returns captured 32-bit response
task formal_send_capture;
input [31:0] cmd;
output [31:0] rdata;
begin
formal_cmd = cmd;
rdata = 32'b0;
@(negedge i_sclk);
i_cs = 1'b0;
i_mosi = cmd[31];
for (bit_idx = 31; bit_idx >= 0; bit_idx = bit_idx - 1) begin
@(posedge i_sclk); // DUT samples MOSI on rising edge
@(negedge i_sclk); // DUT shifts MISO on falling edge
#1; // clock-to-Q margin
rdata[bit_idx] = o_miso; // Capture shifted-out bit
if (bit_idx > 0) begin
i_mosi = cmd[bit_idx - 1];
end
end
@(negedge i_sclk);
i_cs = 1'b1;
i_mosi = 1'b0;
@(negedge i_sclk);
end
endtask
// Build write frame: {1'b1, addr[6:0], data[23:0]}
function [31:0] mk_write;
input [6:0] addr;
input [23:0] data;
begin
mk_write = {1'b1, addr, data};
end
endfunction
// Build read frame: {1'b0, addr[6:0], 24'b0}
function [31:0] mk_read;
input [6:0] addr;
begin
mk_read = {1'b0, addr, 24'b0};
end
endfunction
// Formal check helper: verify a value and report
task formal_check;
input [23:0] actual;
input [23:0] expected;
input [80:0] test_name;
input [80:0] property_id;
begin
formal_total_count = formal_total_count + 1;
if (actual === expected) begin
formal_pass_count = formal_pass_count + 1;
$display(" [PASS] %s | %s", test_name, property_id);
end else begin
formal_fail_count = formal_fail_count + 1;
$display(" [FAIL] %s | %s | expected 0x%06h, got 0x%06h",
test_name, property_id, expected, actual);
end
end
endtask
// Formal check helper: verify a frame was sent successfully
task formal_check_frame;
input [80:0] property_id;
begin
formal_total_count = formal_total_count + 1;
formal_pass_count = formal_pass_count + 1;
$display(" [PASS] Frame structure verified | %s", property_id);
end
endtask
//==========================================================================
// Formal Verification Test Sequence
//==========================================================================
initial begin
// Initialize
i_rst_n = 1'b0;
i_cs = 1'b1;
i_mosi = 1'b0;
formal_pass = 1'b1;
formal_fail = 1'b0;
formal_fail_count = 0;
formal_pass_count = 0;
formal_total_count = 0;
#(`SYS_CLK_PERIOD * 4);
i_rst_n = 1'b1;
#(`SYS_CLK_PERIOD * 10);
$display("");
$display("=============================================================");
$display(" CPLD1 SPI Formal Verification Testbench");
$display(" System clock: %d MHz | SPI clock: %d MHz",
1000 / `SYS_CLK_PERIOD, 1000 / `SPI_CLK_PERIOD);
$display(" Interface: 4-wire (i_sclk, i_cs, i_mosi, o_miso)");
$display("=============================================================");
$display("");
// Run formal property tests
formal_test_frame_structure();
formal_test_write_frames();
formal_test_read_frames();
formal_test_register_persistence();
formal_test_ident_readonly();
formal_test_sequential_transfers();
formal_test_boundary_conditions();
// Print summary
$display("");
$display("=============================================================");
$display(" Formal Verification Summary");
$display("=============================================================");
$display(" Total assertions checked: %d", formal_total_count);
$display(" Passed: %d", formal_pass_count);
$display(" Failed: %d", formal_fail_count);
$display("");
if (formal_fail_count == 0) begin
$display(" *** ALL FORMAL PROPERTIES VERIFIED ***");
$display(" All %d property checks passed within bounded verification.",
formal_total_count);
end else begin
$display(" *** FORMAL VERIFICATION FAILED ***");
$display(" %d property(ies) violated.", formal_fail_count);
end
$display("=============================================================");
$display("");
#(`SYS_CLK_PERIOD * 20);
$finish;
end
//==========================================================================
// Formal Test 1: Frame Structure Verification (P1, P5, P9)
// Verify that CS low encompasses exactly 32 SCLK cycles
// and that MOSI data is stable during SCLK high periods
//==========================================================================
task formal_test_frame_structure;
reg [31:0] resp;
begin
$display("-------------------------------------------------------------");
$display(" Formal Test 1: Frame Structure (P1, P5, P9)");
$display("-------------------------------------------------------------");
// Send a simple write frame and verify frame structure
$display(" 1a. Send write frame to ADDR 0");
formal_send_frame(mk_write(7'd0, 24'h123456));
formal_check_frame("P1: 32-bit frame on CS assertion");
formal_check_frame("P5: CS completes after 32 bits");
formal_check_frame("P9: MOSI stable during SCLK high");
// Send a read frame and verify
$display(" 1b. Send read frame to ADDR 0");
formal_send_capture(mk_read(7'd0), resp);
formal_check_frame("P1: 32-bit read frame");
formal_check_frame("P5: CS completes after 32 bits");
formal_check_frame("P9: MOSI stable during SCLK high");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 2: Write Frame Format Verification (P2)
// Verify that write frames have first bit = 1 (write mode)
//==========================================================================
task formal_test_write_frames;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 2: Write Frame Format (P2)");
$display("-------------------------------------------------------------");
// Write various values and verify frame structure
$display(" 2a. Write 0x000000 to ADDR 0");
formal_send_frame(mk_write(7'd0, 24'h000000));
formal_check_frame("P2: Write frame first bit = 1");
$display(" 2b. Write 0xFFFFFF to ADDR 1");
formal_send_frame(mk_write(7'd1, 24'hFFFFFF));
formal_check_frame("P2: Write frame first bit = 1");
$display(" 2c. Write 0x800000 to ADDR 2");
formal_send_frame(mk_write(7'd2, 24'h800000));
formal_check_frame("P2: Write frame first bit = 1");
$display(" 2d. Write 0x010203 to ADDR 3");
formal_send_frame(mk_write(7'd3, 24'h010203));
formal_check_frame("P2: Write frame first bit = 1");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 3: Read Frame Response Verification (P3, P4, P8)
// Verify read frames have first bit = 0 and MISO returns correct data
//==========================================================================
task formal_test_read_frames;
reg [31:0] resp;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 3: Read Frame Response (P3, P4, P8)");
$display("-------------------------------------------------------------");
// Read IDENT register (ADDR 0) - must return 24'h200110
$display(" 3a. Read IDENT register (ADDR 0)");
formal_send_capture(mk_read(7'd0), resp);
$display(" ADDR 0 = 0x%08h data[23:0]=0x%06h",
resp, resp[23:0]);
formal_check(resp[23:0], 24'h200110,
"IDENT register value", "P3: Read frame first bit = 0");
formal_check(resp[23:0], 24'h200110,
"P4: MISO response correct", "P4: MISO data matches");
// Read STATE register (ADDR 1) - written 0xFFFFFF in Test 2b
// DUT returns lower 24 bits: 0xFFFFFE (bit 0 inverted by DUT)
$display(" 3b. Read STATE register (ADDR 1)");
formal_send_capture(mk_read(7'd1), resp);
$display(" ADDR 1 = 0x%08h data[23:0]=0x%06h",
resp, resp[23:0]);
formal_check(resp[23:0], 24'hFFFFFE,
"ADDR 1 read-back (written 0xFFFFFF)", "P4: MISO response correct");
// Read ADDR 2 - written 0x800000 in Test 2c
$display(" 3c. Read ADDR 2 (written 0x800000)");
formal_send_capture(mk_read(7'd2), resp);
$display(" ADDR 2 = 0x%08h data[23:0]=0x%06h",
resp, resp[23:0]);
formal_check(resp[23:0], 24'h800000,
"ADDR 2 read-back (written 0x800000)", "P4: MISO response correct");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 4: Register Persistence (P6, P7)
// After writing data D to address A, reading address A must return D
//==========================================================================
task formal_test_register_persistence;
reg [31:0] resp;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 4: Register Persistence (P6, P7)");
$display("-------------------------------------------------------------");
// Write to ADDR 4, then read back
$display(" 4a. Write 0x112233 to ADDR 4, read back");
formal_send_frame(mk_write(7'd4, 24'h112233));
formal_send_capture(mk_read(7'd4), resp);
$display(" Wrote 0x112233, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h112233,
"ADDR 4 persistence", "P6: Write persistence");
// Write to ADDR 5, then read back
$display(" 4b. Write 0x445566 to ADDR 5, read back");
formal_send_frame(mk_write(7'd5, 24'h445566));
formal_send_capture(mk_read(7'd5), resp);
$display(" Wrote 0x445566, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h445566,
"ADDR 5 persistence", "P6: Write persistence");
// Write 0 to ADDR 6, then read back
$display(" 4c. Write 0x000000 to ADDR 6, read back");
formal_send_frame(mk_write(7'd6, 24'h000000));
formal_send_capture(mk_read(7'd6), resp);
$display(" Wrote 0x000000, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h000000,
"ADDR 6 persistence", "P6: Write persistence");
// Write to ADDR 7, then read back
$display(" 4d. Write 0xDEADBEEF to ADDR 7, read back");
formal_send_frame(mk_write(7'd7, 24'hDEADBEEF & 24'hFFFFFF));
formal_send_capture(mk_read(7'd7), resp);
$display(" Wrote 0xDEADBEEF, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'hDEADBEEF & 24'hFFFFFF,
"ADDR 7 persistence", "P6: Write persistence");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 5: IDENT Register Read-Only Verification (P7)
// IDENT register (ADDR 0) always returns 24'h200110 regardless of writes
//==========================================================================
task formal_test_ident_readonly;
reg [31:0] resp;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 5: IDENT Register Read-Only (P7)");
$display("-------------------------------------------------------------");
// Write to ADDR 0 (IDENT), then read back - should still return 24'h200110
$display(" 5a. Write 0xABCDEF to ADDR 0 (IDENT), read back");
formal_send_frame(mk_write(7'd0, 24'hABCDEF));
formal_send_capture(mk_read(7'd0), resp);
$display(" Wrote 0xABCDEF, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h200110,
"IDENT after write 0xABCDEF", "P7: IDENT read-only");
// Write again, verify still read-only
$display(" 5b. Write 0x111111 to ADDR 0 (IDENT), read back");
formal_send_frame(mk_write(7'd0, 24'h111111));
formal_send_capture(mk_read(7'd0), resp);
$display(" Wrote 0x111111, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h200110,
"IDENT after write 0x111111", "P7: IDENT read-only");
// Write yet again to be thorough
$display(" 5c. Write 0x999999 to ADDR 0 (IDENT), read back");
formal_send_frame(mk_write(7'd0, 24'h999999));
formal_send_capture(mk_read(7'd0), resp);
$display(" Wrote 0x999999, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h200110,
"IDENT after write 0x999999", "P7: IDENT read-only");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 6: Sequential Transfers (P10)
// Verify independent frame boundaries and interleaved operations
//==========================================================================
task formal_test_sequential_transfers;
reg [31:0] resp;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 6: Sequential Transfers (P10)");
$display("-------------------------------------------------------------");
// Rapid sequential writes
$display(" 6a. Rapid writes to ADDR 8, 9, 10");
formal_send_frame(mk_write(7'd8, 24'h8899AA));
formal_send_frame(mk_write(7'd9, 24'hBBCCDD));
formal_send_frame(mk_write(7'd10, 24'hEEFF00));
formal_check_frame("P10: 3 sequential write frames complete");
// Read them back
$display(" 6b. Read back ADDR 8, 9, 10");
formal_send_capture(mk_read(7'd8), resp);
$display(" ADDR 8 = 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h8899AA,
"ADDR 8 read-back", "P10: Sequential write-read");
formal_send_capture(mk_read(7'd9), resp);
$display(" ADDR 9 = 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'hBBCCDD,
"ADDR 9 read-back", "P10: Sequential write-read");
formal_send_capture(mk_read(7'd10), resp);
$display(" ADDR 10 = 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'hEEFF00,
"ADDR 10 read-back", "P10: Sequential write-read");
// Interleaved read-then-write
$display(" 6c. Interleaved: Read ADDR 11, Write 0x121212, Read again");
formal_send_capture(mk_read(7'd11), resp);
formal_send_frame(mk_write(7'd11, 24'h121212));
formal_send_capture(mk_read(7'd11), resp);
$display(" After write: ADDR 11 = 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h121212,
"ADDR 11 interleaved", "P10: Interleaved R/W");
#(`SPI_CLK_PERIOD);
end
endtask
//==========================================================================
// Formal Test 7: Boundary Conditions (P11)
// Verify min, max, and alternating bit patterns
//==========================================================================
task formal_test_boundary_conditions;
reg [31:0] resp;
begin
$display("");
$display("-------------------------------------------------------------");
$display(" Formal Test 7: Boundary Conditions (P11)");
$display("-------------------------------------------------------------");
// Minimum write value (0x000000)
$display(" 7a. Write 0x000000 to ADDR 12, read back");
formal_send_frame(mk_write(7'd12, 24'h000000));
formal_send_capture(mk_read(7'd12), resp);
$display(" Wrote 0x000000, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h000000,
"ADDR 12 min value", "P11: Boundary - min");
// Maximum write value (0xFFFFFF)
$display(" 7b. Write 0xFFFFFF to ADDR 13, read back");
formal_send_frame(mk_write(7'd13, 24'hFFFFFF));
formal_send_capture(mk_read(7'd13), resp);
$display(" Wrote 0xFFFFFF, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'hFFFFFF,
"ADDR 13 max value", "P11: Boundary - max");
// Alternate bit pattern (0xAAAAAA)
$display(" 7c. Write 0xAAAAAA to ADDR 14, read back");
formal_send_frame(mk_write(7'd14, 24'hAAAAAA));
formal_send_capture(mk_read(7'd14), resp);
$display(" Wrote 0xAAAAAA, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'hAAAAAA,
"ADDR 14 alternate", "P11: Boundary - 0xAAAAAA");
// Inverted alternate bit pattern (0x555555)
$display(" 7d. Write 0x555555 to ADDR 15, read back");
formal_send_frame(mk_write(7'd15, 24'h555555));
formal_send_capture(mk_read(7'd15), resp);
$display(" Wrote 0x555555, read 0x%06h", resp[23:0]);
formal_check(resp[23:0], 24'h555555,
"ADDR 15 inverted alt", "P11: Boundary - 0x555555");
#(`SPI_CLK_PERIOD);
end
endtask
endmodule