Warp-SE/cpld/IOBM.v
2021-10-29 06:04:59 -04:00

124 lines
2.9 KiB
Verilog

module IOBM(
/* PDS interface */
input C16M, input C8M, input E,
output reg nAS, output reg nLDS, output reg nUDS, output reg nVMA,
input nDTACK, input nVPA, input nBERR, input nRES,
/* PDS address and data latch control */
output nAoutOE, output reg nDoutOE, output reg ALE0, output reg nDinLE,
/* IO bus slave port interface */
output reg IOACT, output reg IOBERR, input IOREQ, input IOLDS, input IOUDS, input IOWE);
/* I/O bus slave port input synchronization */
reg IOREQr = 0;
always @(negedge C16M) begin IOREQr <= IOREQ; end
/* DTACK, BERR, RESET synchronization */
reg DTACKrr, DTACKrf, VPArr, VPArf, BERRrr, BERRrf, RESrr, RESrf;
always @(posedge C16M) begin
DTACKrr <= ~nDTACK;
VPArr <= ~nVPA;
BERRrr <= ~nBERR;
RESrr <= ~nRES;
end
always @(negedge C16M) begin
DTACKrf <= ~nDTACK;
VPArf <= ~nVPA;
BERRrf <= ~nBERR;
RESrf <= ~nRES;
end
wire DTACK = DTACKrr && DTACKrf;
wire BERR = BERRrr && BERRrf;
wire VPA = VPArr && VPArf;
wire RES = RESrr && RESrf;
/* E clock state */
reg [4:0] ES;
reg Er;
reg Er2;
always @(negedge C8M) begin Er <= E; end
always @(posedge C16M) begin Er2 <= Er; end
always @(posedge C16M) begin
if (Er2 && ~Er) ES <= 1;
else if (ES==0 || ES==19) ES <= 0;
else ES <= ES+1;
end
/* ETACK and VMA generation */
reg ETACK = 0;
always @(posedge C16M) begin ETACK <= ES==16 && ~nVMA; end
always @(posedge C16M) begin
if (ES==7 && IOACT && VPA) nVMA <= 0;
else if (ES==0) nVMA <= 1;
end
/* I/O bus state */
reg [2:0] IOS = 0;
always @(posedge C16M) begin
if (IOS==0) begin
if (IOREQr) begin
if (~C8M) begin
IOS <= 1;
end else begin
IOS <= 0;
end
IOACT <= 1;
ALE0 <= 1;
end else begin
IOS <= 0;
IOACT <= 0;
ALE0 <= 0;
end
end else if (IOS==1) begin
IOS <= 2;
IOACT <= 1;
ALE0 <= 1;
end else if (IOS==2) begin
IOS <= 3;
IOACT <= 1;
ALE0 <= 1;
end else if (IOS==3) begin
IOS <= 4;
IOACT <= 1;
ALE0 <= 1;
end else if (IOS==4) begin
IOS <= 5;
IOACT <= 1;
ALE0 <= 1;
end else if (IOS==5) begin
if (C8M && (DTACK || ETACK || BERR || RES)) begin
IOS <= 6;
IOACT <= 0;
IOBERR <= ~nBERR;
end else begin
IOS <= 5;
IOACT <= 1;
end
ALE0 <= 1;
end else if (IOS==6) begin
IOS <= 7;
IOACT <= 0;
ALE0 <= 0;
end else if (IOS==7) begin
IOS <= 0;
IOACT <= 0;
ALE0 <= 0;
end
end
/* PDS address and data latch control */
assign nAoutOE = 0;
always @(negedge C16M) begin nDinLE <= IOS==4 || IOS==5; end
always @(posedge C16M) begin
nDoutOE <= ~(IOWE && (IOS==1 || IOS==2 || IOS==3 ||
IOS==4 || IOS==5 || IOS==6));
end
/* AS, DS control */
always @(negedge C16M) begin
nAS <= ~(IOS==1 || IOS==2 || IOS==3 || IOS==4 || IOS==5);
nLDS <= ~(IOLDS && (((IOS==1 || IOS==2) && ~IOWE) || IOS==3 || IOS==4 || IOS==5));
nUDS <= ~(IOUDS && (((IOS==1 || IOS==2) && ~IOWE) || IOS==3 || IOS==4 || IOS==5));
end
endmodule