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hpdmc_banktimer.v
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hpdmc_banktimer.v
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/*
* Milkymist SoC
* Copyright (C) 2007, 2008, 2009 Sebastien Bourdeauducq
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY 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. If not, see <http://www.gnu.org/licenses/>.
*/
module hpdmc_banktimer(
input sys_clk,
input sdram_rst,
input tim_cas,
input [1:0] tim_wr,
input read,
input write,
output reg precharge_safe
);
reg [2:0] counter;
always @(posedge sys_clk) begin
if(sdram_rst) begin
counter <= 3'd0;
precharge_safe <= 1'b1;
end else begin
if(read) begin
/* see p.26 of datasheet :
* "A Read burst may be followed by, or truncated with, a Precharge command
* to the same bank. The Precharge command should be issued x cycles after
* the Read command, where x equals the number of desired data element
* pairs"
*/
counter <= 3'd4;
precharge_safe <= 1'b0;
end else if(write) begin
counter <= {1'b1, tim_wr};
precharge_safe <= 1'b0;
end else begin
if(counter == 3'b1)
precharge_safe <= 1'b1;
if(~precharge_safe)
counter <= counter - 3'b1;
end
end
end
endmodule