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Update genWave to use 24.4 bit fixed point

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Improve frequency target accuracy from 1Hz to 0.0625Hz
This commit is contained in:
Aadi Desai 2023-06-07 23:01:20 +01:00
parent c19b7e625f
commit 4c4d287c63
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2 changed files with 7 additions and 8 deletions
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13
rtl/genWave.sv
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@ -5,8 +5,7 @@ module genWave
, input var i_rst48_n // Active low reset
, input var i_pause // Pause sample generation (backpressure)
, input var [ 5:0] i_osc_sel // Oscillator select, to update target freq / waveform
, input var [23:0] i_t_freq // Target frequency for selected oscillator
// TODO: update this to use fixed point decimal for better accuracy?
, input var [27:0] i_t_freq // Target frequency for selected oscillator (24.4 fixed point)
, input var i_tf_valid // Target frequency valid pulse (i_osc_sel must be set first)
, input var [ 7:0] i_wav_sel // Waveform select for selected oscillator
, input var i_ws_valid // Waveform select valid pulse (i_osc_sel must be set first)
@ -35,7 +34,7 @@ always_comb o_pulse = clk_48k && !clk_48k_past; // Detect rising edge of 48kHz c
// Per Oscillator Settings Capture #################################################################
logic [23:0] t_freq [0:63];
logic [27:0] t_freq [0:63];
always_ff @(posedge i_clk48)
if (i_tf_valid) t_freq[i_osc_sel] <= i_t_freq; // Capture target frequency
@ -50,11 +49,11 @@ always_ff @(posedge i_clk48) // Count to 64 at 48MHz
if (!i_rst48_n) ps_clk <= '0; // Reset
else ps_clk <= ps_clk + 1; // Increment
logic [23:0] int_phase_step; // Phase step calc from target frequency
always_comb int_phase_step = (24'd699 * t_freq[ps_clk]); // 699 = (2^24 / 48000) * 2 (Approximately)
logic [27:0] int_phase_step; // Phase step calc from target frequency
always_comb int_phase_step = (28'd699 * t_freq[ps_clk]); // 699 = (2^24 / 48000) * 2 (Approximately)
logic [15:0] phase_step [0:63]; // Shift step right correctly (2^9)
always_ff @(posedge i_clk48) phase_step[ps_clk] <= {1'b0, int_phase_step[23:9]};
logic [15:0] phase_step [0:63]; // Shift step right correctly (2^9) * (2^4) for fixed point
always_ff @(posedge i_clk48) phase_step[ps_clk] <= {1'b0, int_phase_step[27:13]};
// Per Oscillator Phase Generation #################################################################

2
testWave.py
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@ -20,7 +20,7 @@ class TestWave(Module, AutoCSR, ModuleDoc):
self.pads = pads
self.osc = CSRStorage(size = 6, description = "Index of the Oscillator to Configure (0-63)")
self.tf = CSRStorage(size = 24, description = "Target Frequency of the phase accumulator")
self.tf = CSRStorage(size = 28, description = "Target Frequency of the phase accumulator (24.4 bit fixed point, ie x16)")
self.wav = CSRStorage(size = 8, description = "Waveform to Output (Saw, Square, Triangle, Sine)")
# 48MHz Domain Signals