73 lines
2.3 KiB
Verilog
73 lines
2.3 KiB
Verilog
module nubus_cpldinfpga
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(
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// Control
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input nubus_oe, // disable all 5v drivers
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input tmoen, // tm output enable
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input nubus_master_dir, // direction of signals, i.e. are we in master mode
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// Spares
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input rqst_oe_n, // rqstoen (extra line from FPGA to CPLD)
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// NuBus
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input [3:0] id_n_3v3, // nubus ID of this card to FPGA
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// NuBus Arbiter
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input arbcy_n, // enable arbitter
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input [3:0] arb_n_3v3, // NuBus arbiter's lines
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output [3:0] arb_o_n, // NuBus arbiter's control lines
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output grant, // Grant access
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// Cycle Control (NuBus two-way)
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input tm0_n_3v3, // nubus tm0 to/from FPGA
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output tm0_o_n, // start from NuBus
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input tm1_n_3v3, // nubus tm1 to/from FPGA
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output tm1_o_n, // start from NuBus
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output tmx_oe_n, // start from NuBus
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input tm2_n_3v3, // nubus tm2 to/from FPGA
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output tm2_o_n, // start from NuBus
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output tm2_oe_n, // start from NuBus
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input start_n_3v3, // start to/from FPGA
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output start_o_n, // start from NuBus
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output start_oe_n, // start from NuBus
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input ack_n_3v3, // ack from/to FPGA
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output ack_o_n, // ack to NuBus
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output ack_oe_n, // ack OE NuBus
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// Master Request (OC)
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input rqst_n_3v3, // rqst from/to FPGA
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output rqst_o_n // rqst to NuBus
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);
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// placeholders
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assign tm2_o_n = 0;
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assign tm2_oe_n = 1;
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// ~nubus_master_dir-controlled signals
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assign start_o_n = nubus_oe ? 1 : ( nubus_master_dir ? start_n_3v3 : 1); // master out
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assign start_oe_n = nubus_oe ? 1 : ( nubus_master_dir ? 0 : 1); // master out
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// rqst_o_n is always driven (the 74lvt125 wired as open collector will convert 1 to Z) and is active low
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assign rqst_o_n = nubus_oe ? 1 : (~rqst_oe_n ? rqst_n_3v3 : 1); // master out
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assign ack_o_n = nubus_oe ? 1 : (( ~tmoen) ? ack_n_3v3 : 1); // slave out/in
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assign ack_oe_n = nubus_oe ? 1 : (( ~tmoen) ? 0 : 1); // slave out/in
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assign tm0_o_n = nubus_oe ? 1 : (( ~tmoen) ? tm0_n_3v3 : 1); // slave out/in
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assign tm1_o_n = nubus_oe ? 1 : (( ~tmoen) ? tm1_n_3v3 : 1); // slave out/in
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assign tmx_oe_n = nubus_oe ? 1 : (( ~tmoen) ? 0 : 1); // slave out/in
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nubus_arbiter UArbiter
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(
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.idn(id_n_3v3),
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.arbn(arb_n_3v3),
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.arbon(arb_o_n),
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.arbcyn(arbcy_n),
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.grant(grant)
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);
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endmodule // nubus_cpld
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