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Old 31 July 2012, 18:06   #110
kipper2k
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Join Date: Sep 2006
Location: Thunder Bay, Canada
Posts: 3,616
Quote:
Originally Posted by TotO View Post
I hope that is not the real reason.
I tried to use my cartridge with my 8mb expansion and the A500 won't initialise. once the expansion is removed the AR3 works, if i could change the code in the 8mb (and 4m) board to sit higher i would try it to see if it fixes the problem. I have the source if anyone can recompile it after changing the memory config code. It appears that the AR3 needs to start at mem address $400000

here's the code portion that defines the mem map of the expansion card.

// chip selector decoder
always @*
begin
casex( high_addr )
8'b001xxxxx: // $200000-$3fffff
begin
{which_ras[0],which_ras[1],which_ras[2],which_ras[3]} <= 4'b1000; // /RAS0
mem_selected <= 1'b1;
end

8'b010xxxxx: // $400000-$5fffff
begin
{which_ras[0],which_ras[1],which_ras[2],which_ras[3]} <= 4'b0100; // /RAS1
mem_selected <= 1'b1;
end

// remove this two CASE sections below for 4Mb only decoding (do not remove "default:"!)
8'b011xxxxx: // $600000-$7fffff
begin
{which_ras[0],which_ras[1],which_ras[2],which_ras[3]} <= 4'b0010; // /RAS2
mem_selected <= 1'b1;
end

8'b100xxxxx: // $800000-$9fffff
begin
{which_ras[0],which_ras[1],which_ras[2],which_ras[3]} <= 4'b0001; // /RAS3
mem_selected <= 1'b1;
end

default:
begin
{which_ras[0],which_ras[1],which_ras[2],which_ras[3]} <= 4'b0000; // nothing
mem_selected <= 1'b0;
end

endcase
end

Last edited by kipper2k; 31 July 2012 at 18:12.
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