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[/] [xulalx25soc/] [trunk/] [rtl/] [spiarbiter.v] - Rev 7
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/////////////////////////////////////////////////////////////////////////// // // Filename: spiarbiter.v // // Project: XuLA2 board // // Purpose: The XuLA2 offers SPI access to both a FLASH and an SD Card. // This simple script arbitrates between the two of those to // determine who has access. Drivers for both chips may interact with // this arbiter as though it were a SPI device with one additional piece // of functionality: the clock line may not be brought low until access // has been granted to the chip. Thus, the controller wishing to access // its device should pull the CS line low, and then wait to read that // its grant line is high. Once CS is low and grant is high, it may // then bring CK low and start its transaction. // // When two or more controllers request access at the same time, // access will be given in priority order. Further, access is always // granted to device 'A' without request as long as device 'B' isn't // busy. // // // 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. // // License: GPL, v3, as defined and found on www.gnu.org, // http://www.gnu.org/licenses/gpl.html // // /////////////////////////////////////////////////////////////////////////// // // module spiarbiter(i_clk, i_cs_a_n, i_ck_a, i_mosi_a, i_cs_b_n, i_ck_b, i_mosi_b, o_cs_a_n, o_cs_b_n, o_ck, o_mosi); // , i_en, o_err input i_clk; input i_cs_a_n, i_ck_a, i_mosi_a; // output wire o_grant_a; input i_cs_b_n, i_ck_b, i_mosi_b; // output wire o_grant_b; output wire o_cs_a_n, o_cs_b_n, o_ck, o_mosi; reg a_owner; initial a_owner = 1'b1; always @(posedge i_clk) if ((i_cs_a_n)&&(i_cs_b_n)) a_owner <= 1'b1; // Keep control else if ((i_cs_a_n)&&(~i_cs_b_n)) a_owner <= 1'b0; // Give up control // assign o_grant_a = a_owner; // assign o_grant_b = (~a_owner); assign o_cs_a_n = (~a_owner)||(~i_cs_a_n); assign o_cs_b_n = ( a_owner)||(~i_cs_b_n); assign o_ck = ( a_owner)?i_ck_a : i_ck_b; assign o_mosi = ( a_owner)?i_mosi_a : i_mosi_b; endmodule
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