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// Assumes a GPMC cycle with GPMC clock, as in the timing diagrams
// If a packet bigger or smaller than we are told is sent, behavior is undefined.
// If dst_rdy_i is low when we get data, behavior is undefined and we signal bus error.
// If there is a bus error, we should be reset
module gpmc_to_fifo_sync
(input arst,
input EM_CLK, input [15:0] EM_D, input [1:0] EM_NBE,
input EM_NCS, input EM_NWE,
output reg [17:0] data_o, output reg src_rdy_o, input dst_rdy_i,
input [15:0] frame_len, input [15:0] fifo_space, output fifo_ready,
output reg bus_error);
reg [10:0] counter;
wire first_write = (counter == 0);
wire last_write = ((counter+1) == frame_len);
wire do_write = ~EM_NCS & ~EM_NWE;
always @(posedge EM_CLK or posedge arst)
if(arst)
data_o <= 0;
else if(do_write)
begin
data_o[15:0] <= EM_D;
data_o[16] <= first_write;
data_o[17] <= last_write;
// no byte writes data_o[18] <= |EM_NBE; // mark half full if either is not enabled FIXME
end
always @(posedge EM_CLK or posedge arst)
if(arst)
src_rdy_o <= 0;
else if(do_write & ~bus_error) // Don't put junk in if there is a bus error
src_rdy_o <= 1;
else
src_rdy_o <= 0; // Assume it was taken, ignore dst_rdy_i
always @(posedge EM_CLK or posedge arst)
if(arst)
counter <= 0;
else if(do_write)
if(last_write)
counter <= 0;
else
counter <= counter + 1;
assign fifo_ready = first_write & (fifo_space > frame_len);
always @(posedge EM_CLK or posedge arst)
if(arst)
bus_error <= 0;
else if(src_rdy_o & ~dst_rdy_i)
bus_error <= 1;
// must be reset to make the error go away
endmodule // gpmc_to_fifo_sync
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