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[/] [xulalx25soc/] [trunk/] [rtl/] [wbscopc.v] - Rev 98
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/////////////////////////////////////////////////////////////////////////// // // Filename: wbscopc.v // // Project: FPGA Library of Routines // // Purpose: This scope is identical in function to the wishbone scope // found in wbscope, save that the output is compressed and that (as a // result) it can only handle recording 31 bits at a time. This allows // the top bit to indicate an 'address difference'. Okay, there's // another difference as well: this version only works in a synchronous // fashion with the clock from the WB bus. You cannot have a separate // bus and data clock. // // Reading/decompressing the output of this scope works in this fashion: // Once the scope has stopped, read from the port. Any time the high // order bit is set, the other 31 bits tell you how many times to repeat // the last value. If the high order bit is not set, then the value // is a new data value. // // I've provided this version of a compressed scope to OpenCores for // discussion purposes. While wbscope.v works and works well by itself, // this compressed scope has a couple of fundamental flaw that I have // yet to fix. One of them is that it is impossible to know when the // trigger took place. The second problem is that it may be impossible // to know the state of the scope at the beginning of the buffer--should // the buffer begin with an address difference value instead of a data // value. // // Ideally, the first item read out of the scope should be a data value, // even if the scope was skipping values to a new address at the time. // If it was in the middle of a skip, the next item out of the scope // should be the skip length. This, though, violates the rule that there // are (1<<LGMEMLEN) items in the memory, and that the trigger took place // on the last item of memory ... so that portion of this compressed // scope is still to be defined. // // Like I said, this version is placed here for discussion purposes, // not because it runs well nor because I have recognized that it has any // particular value (yet). // // Well, I take that back. When dealing with an interface such as the // PS/2 interface, or even the 16x2 LCD interface, it is often true // that things change _very_ slowly. They could change so slowly that // the other approach to the scope doesn't work. This then gives you // a working scope, by only capturing the changes. You'll still need // to figure out (after the fact) when the trigge took place. Perhaps // you'll wish to add the trigger as another data line, so you can find // when it took place in your own data? // // Okay, I take that back twice: I'm finding this compressed scope very // valuable for evaluating the timing associated with a GPS PPS and // associated NMEA stream. I need to collect over a seconds worth of // data, and I don't have enough memory to handle one memory value per // clock, yet I still want to know exactly when the GPS PPS goes high, // when it goes low, when I'm adjusting my clock, and when the clock's // PPS output goes high. Did I synchronize them well? Oh, and when does // the NMEA time string show up when compared with the PPS? All of those // are valuable, but could never be done if the scope wasn't compressed. // // 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 wbscopc(i_clk, i_ce, i_trigger, i_data, i_wb_clk, 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_interrupt); parameter LGMEM = 5'd10, NELM=31, BUSW = 32, SYNCHRONOUS=1; // The input signals that we wish to record input i_clk, i_ce, i_trigger; input [(NELM-1):0] i_data; // The WISHBONE bus for reading and configuring this scope input i_wb_clk, i_wb_cyc, i_wb_stb, i_wb_we; input i_wb_addr; // One address line only input [(BUSW-1):0] i_wb_data; output wire o_wb_ack, o_wb_stall; output wire [(BUSW-1):0] o_wb_data; // And, finally, for a final flair --- offer to interrupt the CPU after // our trigger has gone off. This line is equivalent to the scope // being stopped. It is not maskable here. output wire o_interrupt; // Let's first see how far we can get by cheating. We'll use the // wbscope program, and suffer a lack of several features // When is the full scope reset? Capture that reset bit from any // write. wire lcl_reset; assign lcl_reset = (i_wb_cyc)&&(i_wb_stb)&&(~i_wb_addr)&&(i_wb_we) &&(~i_wb_data[31]); // A big part of this scope is the 'address' of any particular // data value. As of this current version, the 'address' changed // in definition from an absolute time (which had all kinds of // problems) to a difference in time. Hence, when the address line // is high on decompression, the 'address' field will record an // address difference. // // To implement this, we set our 'address' to zero any time the // data changes, but increment it on all other clocks. Should the // address difference get to our maximum value, we let it saturate // rather than overflow. reg [(BUSW-2):0] ck_addr; reg [(NELM-1):0] lst_dat; initial ck_addr = 0; always @(posedge i_clk) if ((lcl_reset)||((i_ce)&&(i_data != lst_dat))) ck_addr <= 0; else if (&ck_addr) ; // Saturated (non-overflowing) address diff else ck_addr <= ck_addr + 1; // // To do our compression, we keep track of two registers: the most // recent data to the device (imm_ prefix) and the data from one // clock ago. This allows us to suppress writes to the scope which // would otherwise be two address writes in a row. reg imm_adr, lst_adr; // Is this an address (1'b1) or data value? reg [(BUSW-2):0] lst_val, // Data for the scope, delayed by one imm_val; // Data to write to the scope initial lst_dat = 0; initial lst_adr = 1'b1; initial imm_adr = 1'b1; always @(posedge i_clk) if (lcl_reset) begin imm_val <= 31'h0; imm_adr <= 1'b1; lst_val <= 31'h0; lst_adr <= 1'b1; lst_dat <= 0; end else if ((i_ce)&&(i_data != lst_dat)) begin imm_val <= { {(BUSW-1-NELM){1'b0}}, i_data }; imm_adr <= 1'b0; lst_val <= imm_val; lst_adr <= imm_adr; lst_dat <= i_data; end else begin imm_val <= ck_addr; // Minimum value here is '1' imm_adr <= 1'b1; lst_val <= imm_val; lst_adr <= imm_adr; end // // Here's where we suppress writing pairs of address words to the // scope at once. // reg r_ce; reg [(BUSW-1):0] r_data; initial r_ce = 1'b0; always @(posedge i_clk) r_ce <= (~lst_adr)||(~imm_adr); always @(posedge i_clk) r_data <= ((~lst_adr)||(~imm_adr)) ? { lst_adr, lst_val } : { {(32 - NELM){1'b0}}, i_data }; // // The trigger needs some extra attention, in order to keep triggers // that happen between events from being ignored. // wire w_trigger; assign w_trigger = (r_trigger)||(i_trigger); reg r_trigger; initial r_trigger = 1'b0; always @(posedge i_clk) if (lcl_reset) r_trigger <= 1'b0; else r_trigger <= w_trigger; // // Call the regular wishbone scope to do all of our real work, now // that we've compressed the input. // wbscope #(.SYNCHRONOUS(1), .LGMEM(LGMEM), .BUSW(BUSW)) cheatersscope(i_clk, r_ce, w_trigger, r_data, i_wb_clk, 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_interrupt); endmodule
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