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[/] [xulalx25soc/] [trunk/] [rtl/] [wbpwmaudio.v] - Rev 39
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/////////////////////////////////////////////////////////////////////////// // // Filename: wbpwmaudio.v // // Project: A Wishbone Controlled PWM (audio) controller // // Purpose: This PWM controller was designed with audio in mind, although // it should be sufficient for many other purposes. Specifically, // it creates a pulse-width modulated output, where the amount of time // the output is 'high' is determined by the pulse width data given to // it. Further, the 'high' time is spread out in bit reversed order. // In this fashion, a halfway point will alternate between high and low, // rather than the normal fashion of being high for half the time and then // low. This approach was chosen to move the PWM artifacts to higher, // inaudible frequencies and hence improve the sound quality. // // The interface supports two addresses: // // Addr[0] is the data register. Writes to this register will set // a 16-bit sample value to be produced by the PWM logic. // Reads will also produce, in the 17th bit, whether the interrupt // is set or not. (If set, it's time to write a new data value // ...) // // Addr[1] is a timer reload value, used to determine how often the // PWM logic needs its next value. This number should be set // to the number of clock cycles between reload values. So, // for example, an 80 MHz clock can generate a 44.1 kHz audio // stream by reading in a new sample every (80e6/44.1e3 = 1814) // samples. After loading a sample, the device is immediately // ready to load a second. Once the first sample completes, // the second sample will start going to the output, and an // interrupt will be generated indicating that the device is // now ready for the third sample. (The one sample buffer // allows some flexibility in getting the new sample there fast // enough ...) // // // If you read through the code below, you'll notice that you can also // set the timer reload value to an immutable constant by changing the // VARIABLE_RATE parameter to 0. When VARIABLE_RATE is set to zero, // both addresses become the same, Addr[0] or the data register, and the // reload value can no longer be changed--forcing the sample rate to // stay constant. // // // Of course, if you don't want to deal with the interrupts or sample // rates, you can still get a pseudo analog output by just setting the // value to the analog output you would like and then not updating // it. In this case, you could also shut the interrupt down at the // controller, to keep that from bothering you as well. // // Creator: Dan Gisselquist, Ph.D. // Gisselquist Technology, LLC // /////////////////////////////////////////////////////////////////////////// // // Copyright (C) 2015, Gisselquist Technology, LLC // // This program is free software (firmware): you can redistribute it and/or // modify it under the terms of the GNU General Public License as published // by the Free Software Foundation, either version 3 of the License, or (at // your option) any later version. // // This program is distributed in the hope that it will be useful, but WITHOUT // ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License // for more details. // // You should have received a copy of the GNU General Public License along // with this program. (It's in the $(ROOT)/doc directory. Run make with no // target there if the PDF file isn't present.) If not, see // <http://www.gnu.org/licenses/> for a copy. // // License: GPL, v3, as defined and found on www.gnu.org, // http://www.gnu.org/licenses/gpl.html // // /////////////////////////////////////////////////////////////////////////// module wbpwmaudio(i_clk, // Wishbone interface i_wb_cyc, i_wb_stb, i_wb_we, i_wb_addr, i_wb_data, o_wb_ack, o_wb_stall, o_wb_data, o_pwm, o_int); parameter DEFAULT_RELOAD = 32'd1814, // about 44.1 kHz @ 80MHz //DEFAULT_RELOAD = 32'd2268,//about 44.1 kHz @ 100MHz VARIABLE_RATE=0; input i_clk; input i_wb_cyc, i_wb_stb, i_wb_we; input i_wb_addr; input [31:0] i_wb_data; output reg o_wb_ack; output wire o_wb_stall; output wire [31:0] o_wb_data; output reg o_pwm; output reg o_int; // How often shall we create an interrupt? Every reload_value clocks! // If VARIABLE_RATE==0, this value will never change and will be kept // at the default reload rate (44.1 kHz, for a 100 MHz clock) generate if (VARIABLE_RATE != 0) begin reg [31:0] r_reload_value; initial r_reload_value = DEFAULT_RELOAD; always @(posedge i_clk) // Data write if ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_addr)&&(i_wb_we)) reload_value <= i_wb_data; wire [31:0] w_reload_value; assign w_reload_value = r_reload_value; end else begin wire [31:0] w_reload_value; assign w_reload_value = DEFAULT_RELOAD; end endgenerate reg [31:0] reload_value, timer; initial reload_value = DEFAULT_RELOAD; always @(posedge i_clk) if (timer == 0) timer <= reload_value; else timer <= timer - 1; reg [15:0] sample_out; always @(posedge i_clk) if (timer == 0) sample_out <= next_sample; reg [15:0] next_sample; reg next_valid; initial next_valid = 1'b1; initial next_sample = 16'h8000; always @(posedge i_clk) // Data write if ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_we) &&((~i_wb_addr)||(VARIABLE_RATE==0))) begin // Write with two's complement data, convert it // internally to binary offset next_sample <= { ~i_wb_data[15], i_wb_data[14:0] }; next_valid <= 1'b1; end else if (timer == 0) next_valid <= 1'b0; initial o_int = 1'b0; always @(posedge i_clk) o_int <= (~next_valid); reg [15:0] pwm_counter; initial pwm_counter = 16'h00; always @(posedge i_clk) pwm_counter <= pwm_counter + 1; wire [15:0] br_counter; genvar k; generate for(k=0; k<16; k=k+1) begin : bit_reversal_loop assign br_counter[k] = pwm_counter[15-k]; end endgenerate always @(posedge i_clk) o_pwm <= (sample_out >= br_counter); generate if (VARIABLE_RATE == 0) begin assign o_wb_data = { 15'h00, o_int, sample_out }; end else begin reg [31:0] r_wb_data; always @(posedge i_clk) if (i_wb_addr) r_wb_data <= reload_value; else r_wb_data <= { 15'h00, o_int, sample_out }; assign o_wb_data = r_wb_data; end endgenerate initial o_wb_ack = 1'b0; always @(posedge i_clk) o_wb_ack <= (i_wb_cyc)&&(i_wb_stb); assign o_wb_stall = 1'b0; endmodule
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