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Merge pull request #117 from NawfalMotii79/fix/agc-gain-arithmetic-overflow

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fix(fpga): widen AGC gain arithmetic to 6-bit to prevent wraparound
This commit is contained in:
Jason
2026-04-21 00:26:33 +03:00
committed by GitHub
parent 607399ec28 3366ac6417
commit 2e9a848908
1 changed files with 7 additions and 7 deletions
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9_Firmware/9_2_FPGA/rx_gain_control.v
+7 -7
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@@ -169,11 +169,11 @@ endfunction
// ========================================================================= // =========================================================================
// Clamp a wider signed value to [-7, +7] // Clamp a wider signed value to [-7, +7]
function signed [3:0] clamp_gain; function signed [3:0] clamp_gain;
input signed [4:0] val; // 5-bit to handle overflow from add input signed [5:0] val; // 6-bit: covers [-22,+22] (max |gain|+step = 7+15)
begin begin
if (val > 5'sd7) if (val > 6'sd7)
clamp_gain = 4'sd7; clamp_gain = 4'sd7;
else if (val < -5'sd7) else if (val < -6'sd7)
clamp_gain = -4'sd7; clamp_gain = -4'sd7;
else else
clamp_gain = val[3:0]; clamp_gain = val[3:0];
@@ -246,15 +246,15 @@ always @(posedge clk or negedge reset_n) begin
// Use inclusive counts/peaks (accounting for simultaneous valid_in) // Use inclusive counts/peaks (accounting for simultaneous valid_in)
if (wire_frame_sat_incr || frame_sat_count > 8'd0) begin if (wire_frame_sat_incr || frame_sat_count > 8'd0) begin
// Clipping detected: reduce gain immediately (attack) // Clipping detected: reduce gain immediately (attack)
agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain}) - agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain[3], agc_gain}) -
$signed({1'b0, agc_attack})); $signed({2'b00, agc_attack}));
holdoff_counter <= agc_holdoff; // Reset holdoff holdoff_counter <= agc_holdoff; // Reset holdoff
end else if ((wire_frame_peak_update ? max_iq[14:7] : frame_peak[14:7]) end else if ((wire_frame_peak_update ? max_iq[14:7] : frame_peak[14:7])
< agc_target) begin < agc_target) begin
// Signal too weak: increase gain after holdoff expires // Signal too weak: increase gain after holdoff expires
if (holdoff_counter == 4'd0) begin if (holdoff_counter == 4'd0) begin
agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain}) + agc_gain <= clamp_gain($signed({agc_gain[3], agc_gain[3], agc_gain}) +
$signed({1'b0, agc_decay})); $signed({2'b00, agc_decay}));
end else begin end else begin
holdoff_counter <= holdoff_counter - 4'd1; holdoff_counter <= holdoff_counter - 4'd1;
end end