something wrong in audio

[LMN128]

Hi, I have something strange in audio signal. It looks like some bits are not reflected or are mixed up. I tried sawtooth example with some changes. Code is here:

logic signed [15:0] audio_sample_word = 16'sd0;
logic signed [15:0] audio_sample_word_minus = 16'sd0;
always @(posedge audio_clk) // Sawtooth wave
begin
  audio_sample_word <= audio_sample_word + 16'sd1;
  audio_sample_word_minus <= audio_sample_word_minus - 16'sd128;
end  
..
hdmi #(.VIDEO_ID_CODE(17), .VIDEO_REFRESH_RATE(50), .AUDIO_RATE(48000), .AUDIO_BIT_WIDTH(16)) hdmi(
 ...
  .clk_pixel(clk_pixel),
  .clk_audio(audio_clk),
  .rgb(rgb),
  .audio_sample_word({audio_sample_word,audio_sample_word_minus}), 

result is here:

This exaple is for 16bits audio. I have found when want use 24bits the highest two bits are not reflected and have to use this: .audio_sample_word({{2'b0,audio_r,6'b0},{2'b0,audio_l,6'b0}}), Could you help me with this issue, please.

[sameer]

Hi Jan,

I'm not aware of any particular logic that would cause that. Could you share the changes you made to that code to use 24 bit audio? That way I can look into this issue with the top testbench. Also, did you already try using a non-signed representation?

[LMN128]

Hi Sameer, sorry for confusion second problem is not related to 24bits audio, but with 44100Hz sample rate. I use this code:

logic clk_audio;
logic [8:0] audio_divider;

always_ff@(posedge clk_pixel) 
begin
if (audio_divider<9'd306-1) audio_divider++; //generated from clk_pixel 27.0000MHz/281=48042,70Hz ; 27.0000MHz/306=44117,64Hz
else  begin clk_audio<=~clk_audio; audio_divider<=0; end
end

logic [23:0] audio_sample_word [1:0] = '{24'sd0, 24'sd0};
always_ff@(posedge clk_audio)
begin
audio_sample_word[0] <= audio_sample_word[0] + 128;  //sawtooth generator
audio_sample_word[1] <= audio_sample_word[1] - 256;  
end 

logic [23:0] rgb = 24'd0;
logic [9:0] cx, cy, screen_start_x, screen_start_y, frame_width, frame_height, screen_width, screen_height;
// Border test (left = red, top = green, right = blue, bottom = blue, fill = black)
always_ff@(posedge clk_pixel)
  rgb <= {cx == screen_start_x ? ~8'd0 : 8'd0, cy == screen_start_y ? ~8'd0 : 8'd0, cx == frame_width - 1'd1 || cy == frame_height - 1'd1 ? ~8'd0 : 8'd0};

hdmi #(.VIDEO_ID_CODE(17), .VIDEO_REFRESH_RATE(50), .AUDIO_RATE(44100), .AUDIO_BIT_WIDTH(24)) hdmi(
  .clk_pixel_x10(clk_pixel_x10),
  .clk_pixel(clk_pixel),
  .clk_audio(clk_audio),
  .rgb(rgb),
  .audio_sample_word(audio_sample_word),
  .tmds_p(dvdata_p),
  .tmds_clock_p(dvclk_p),
  .tmds_n(dvdata_n),
  .tmds_clock_n(dvclk_n),
  .cx(cx),
  .cy(cy),
  .screen_start_x(screen_start_x),
  .screen_start_y(screen_start_y),
  .frame_width(frame_width),
  .frame_height(frame_height),
  .screen_width(screen_width),
  .screen_height(screen_height)
);

and look at how is signal produced. When I change sample rate to 48000Hz the signal has nice sawtooth shape.

[mopplayer]

Hi,

l think you are successful to set up and show.

I use the test pattern to test, there are always two block shown.

Is my screen not supported? or something wrong?

Did you have some ideas?

https://imgur.com/ArIkfPk

[sameer]

Hi mopplayer,

Could you create a separate issue for this? Also, what model of TV/monitor are you using?

On Wed, Sep 14, 2022, at 19:42, mopplayer wrote:

Hi,

l think you are successful to set up and show.

I use the test pattern to test, there are always two block shown.

Is my screen not supported? or something wrong?

Did you have some ideas?

https://imgur.com/ArIkfPk

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[mopplayer]

Hi @sameer,

I have created another issue.

Thank you very much.

[sameer]

Should be resolved by https://github.com/hdl-util/hdmi/commit/08936f65be09abac338cd8c13beee289af7e7e59