or1200_iwb_biu.v

or1200开源risc cpu的verilog描述实现

		previous_complete <= #1 1'b1;
	else if ((biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~aborted & ~(wb_stb_o & ~wb_ack_i))
		previous_complete <= #1 1'b0;

//
// Input data bus
//
`ifdef OR1200_REGISTERED_INPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		biu_dat_o <= #1 32'h0000_0000;
	else if (wb_ack_i)
		biu_dat_o <= #1 wb_dat_i;
`else
assign biu_dat_o = repeated_access_ack ? wb_dat_r : wb_dat_i;
`endif

//
// Output data bus
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_dat_o <= #1 {dw{1'b0}};
	else if ((biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~aborted)
		wb_dat_o <= #1 biu_dat_i;
`else
assign wb_dat_o = biu_dat_i;
`endif

//
// Valid_div counts RISC clock cycles by modulo 4
// and is used to synchronize external WB i/f to
// RISC clock
//
always @(posedge clk or posedge rst)
	if (rst)
		valid_div <= #1 2'b0;
	else
		valid_div <= #1 valid_div + 1'd1;

//
// biu_ack_o is one RISC clock cycle long long_ack_o.
// long_ack_o is one, two or four RISC clock cycles long because
// WISHBONE can work at 1, 1/2 or 1/4 RISC clock.
//
assign biu_ack_o = (repeated_access_ack | long_ack_o) & ~aborted_r
`ifdef OR1200_CLKDIV_2_SUPPORTED
		& (valid_div[0] | ~clmode[0])
`ifdef OR1200_CLKDIV_4_SUPPORTED
		& (valid_div[1] | ~clmode[1])
`endif
`endif
		;

//
// Acknowledgment of the data to the RISC
//
// long_ack_o
//
`ifdef OR1200_REGISTERED_INPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		long_ack_o <= #1 1'b0;
	else
		long_ack_o <= #1 wb_ack_i & ~aborted;
`else
assign long_ack_o = wb_ack_i;
`endif

//
// biu_err_o is one RISC clock cycle long long_err_o.
// long_err_o is one, two or four RISC clock cycles long because
// WISHBONE can work at 1, 1/2 or 1/4 RISC clock.
//
assign biu_err_o = long_err_o
`ifdef OR1200_CLKDIV_2_SUPPORTED
		& (valid_div[0] | ~clmode[0])
`ifdef OR1200_CLKDIV_4_SUPPORTED
		& (valid_div[1] | ~clmode[1])
`endif
`endif
		;

//
// Error termination
//
// long_err_o
//
`ifdef OR1200_REGISTERED_INPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		long_err_o <= #1 1'b0;
	else
		long_err_o <= #1 wb_err_i & ~aborted;
`else
assign long_err_o = wb_err_i & ~aborted_r;
`endif

//
// Retry counter
//
// Assert 'retry' when 'wb_rty_i' is sampled high and keep it high
// until retry counter doesn't expire
// 
`ifdef OR1200_WB_RETRY
assign retry = wb_rty_i | (|retry_cntr);
`else
assign retry = 1'b0;
`endif
`ifdef OR1200_WB_RETRY
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		retry_cntr <= #1 1'b0;
	else if (wb_rty_i)
		retry_cntr <= #1 {`OR1200_WB_RETRY{1'b1}};
	else if (retry_cntr)
		retry_cntr <= #1 retry_cntr - 7'd1;
`endif

//
// Graceful completion of aborted transfers
//
// Assert 'aborted' when 1) current transfer is in progress (wb_stb_o; which
// we know is only asserted together with wb_cyc_o) 2) and in next WB clock cycle
// wb_stb_o would be deasserted (biu_cyc_i and biu_stb_i are low) 3) and
// there is no termination of current transfer in this WB clock cycle (wb_ack_i
// and wb_err_i are low).
// 'aborted_r' is registered 'aborted' and extended until this "aborted" transfer
// is properly terminated with wb_ack_i/wb_err_i.
// 
assign aborted = wb_stb_o & ~(biu_cyc_i & biu_stb_i) & ~(wb_ack_i | wb_err_i);
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		aborted_r <= #1 1'b0;
	else if (wb_ack_i | wb_err_i)
		aborted_r <= #1 1'b0;
	else if (aborted)
		aborted_r <= #1 1'b1;

//
// WB cyc_o
//
// Either 1) normal transfer initiated by biu_cyc_i (and biu_cab_i if
// bursts are enabled) and possibly suspended by 'retry'
// or 2) extended "aborted" transfer
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_cyc_o <= #1 1'b0;
	else
`ifdef OR1200_NO_BURSTS
		wb_cyc_o <= #1 biu_cyc_i & ~wb_ack_i & ~retry & ~repeated_access | aborted & ~wb_ack_i;
`else
		wb_cyc_o <= #1 biu_cyc_i & ~wb_ack_i & ~retry & ~repeated_access | biu_cab_i | aborted & ~wb_ack_i;
`endif
`else
`ifdef OR1200_NO_BURSTS
assign wb_cyc_o = biu_cyc_i & ~retry;
`else
assign wb_cyc_o = biu_cyc_i | biu_cab_i & ~retry;
`endif
`endif

//
// WB stb_o
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_stb_o <= #1 1'b0;
	else
		wb_stb_o <= #1 (biu_cyc_i & biu_stb_i) & ~wb_ack_i & ~retry & ~repeated_access | aborted & ~wb_ack_i;
`else
assign wb_stb_o = biu_cyc_i & biu_stb_i;
`endif

//
// WB we_o
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_we_o <= #1 1'b0;
	else
		wb_we_o <= #1 biu_cyc_i & biu_stb_i & biu_we_i | aborted & wb_we_o;
`else
assign wb_we_o = biu_cyc_i & biu_stb_i & biu_we_i;
`endif

//
// WB sel_o
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_sel_o <= #1 4'b0000;
	else
		wb_sel_o <= #1 biu_sel_i;
`else
assign wb_sel_o = biu_sel_i;
`endif

`ifdef OR1200_WB_CAB
//
// WB cab_o
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_cab_o <= #1 1'b0;
	else
		wb_cab_o <= #1 biu_cab_i;
`else
assign wb_cab_o = biu_cab_i;
`endif
`endif

`ifdef OR1200_WB_B3
//
// Count burst beats
//
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		burst_len <= #1 2'b00;
	else if (biu_cab_i && burst_len && wb_ack_i)
		burst_len <= #1 burst_len - 1'b1;
	else if (~biu_cab_i)
		burst_len <= #1 2'b11;

//
// WB cti_o
//
`ifdef OR1200_REGISTERED_OUTPUTS
always @(posedge wb_clk_i or posedge wb_rst_i)
	if (wb_rst_i)
		wb_cti_o <= #1 3'b000;	// classic cycle
`ifdef OR1200_NO_BURSTS
	else
		wb_cti_o <= #1 3'b111;	// end-of-burst
`else
	else if (biu_cab_i && burst_len[1])
		wb_cti_o <= #1 3'b010;	// incrementing burst cycle
	else if (biu_cab_i && wb_ack_i)
		wb_cti_o <= #1 3'b111;	// end-of-burst
`endif	// OR1200_NO_BURSTS
`else
Unsupported !!!;
`endif

//
// WB bte_o
//
assign wb_bte_o = 2'b01;	// 4-beat wrap burst

`endif	// OR1200_WB_B3

endmodule