// ZXiznet project
// (c) NedoPC 2012
//
// zx-bus functions: ports mapping/access, ROM mapping
module zbus
(
input wire [15:0] za,
inout wire [ 7:0] zd,
//
inout wire [ 7:0] bd,
//
input wire ziorq_n,
input wire zrd_n,
input wire zwr_n,
input wire zmreq_n,
output wire ziorqge,
output wire zblkrom,
input wire zcsrom_n,
input wire zrst_n,
//
output wire ports_wrena,
output wire ports_wrstb_n,
output wire [ 1:0] ports_addr,
output wire [ 7:0] ports_wrdata,
input wire [ 7:0] ports_rddata,
//
input wire [ 1:0] rommap_win,
input wire rommap_ena,
//
output wire sl811_cs_n,
output wire sl811_a0,
//
output wire w5300_cs_n,
input wire w5300_ports
);
parameter BASE_ADDR = 8'hAB;
wire io_addr_ok;
wire mrd, mwr;
wire ena_dbuf;
wire ena_din;
wire ena_dout;
// addr decode
assign io_addr_ok = (za[7:0]==BASE_ADDR);
// IORQGE
assign ziorqge = io_addr_ok ? 1'b1 : 1'bZ;
// ports write
assign ports_addr = za[9:8];
//
assign ports_wrdata = zd;
//
assign ports_wrena = io_addr_ok && za[15];
assign ports_wrstb_n = ziorq_n | zwr_n;
// sl811 chip select and A0
assign sl811_cs_n = !( !w5300_ports && io_addr_ok && ( !za[15] || (za[15] && za[9:8]==2'b00) ) && !ziorq_n );
//
assign sl811_a0 = ~za[15];
// w5300 chip select
assign mwr = !zmreq_n && !zwr_n && (za[15:14]==rommap_win) && rommap_ena;
assign mrd = !zmreq_n && !zrd_n && !zcsrom_n && (za[15:14]==rommap_win) && rommap_ena;
//
assign w5300_cs_n = ~(mwr || mrd || ( w5300_ports && io_addr_ok && !za[15] && !ziorq_n ) );
// block ROM
assign zblkrom = (rommap_ena && (za[15:14]==rommap_win)) ? 1'b1 : 1'bZ;
assign ena_dbuf = (~sl811_cs_n) | (~w5300_cs_n);
assign ena_din = ~zwr_n;
assign ena_dout = ~zrd_n;
// ports data read/buffering
assign zd = (io_addr_ok && !ziorq_n && !zrd_n && za[15] && (za[9:8]!=2'b00)) ?
ports_rddata : ( (ena_dbuf && ena_dout) ? bd : 8'bZZZZ_ZZZZ );
assign bd = (ena_dbuf && ena_din) ? zd : 8'bZZZZ_ZZZZ;
endmodule