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nix-servo/fast-servo/linien-gateware/verilog/axi_slave.v

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/**
* $Id: axi_slave.v 961 2014-01-21 11:40:39Z matej.oblak $
*
* @brief Red Pitaya symplified AXI slave.
*
* @Author Matej Oblak
*
* (c) Red Pitaya http://www.redpitaya.com
*
* This part of code is written in Verilog hardware description language (HDL).
* Please visit http://en.wikipedia.org/wiki/Verilog
* for more details on the language used herein.
*/
/**
* GENERAL DESCRIPTION:
*
* AXI slave used also for simple bus master.
*
*
* /------\
* WR ADDRESS ----> | WR |
* WR DATA ----> | | -----------
* WR RESPONSE <---- | CH | |
* \------/ /--------\
* | SIMPLE | ---> WR/RD ADDRRESS
* AXI | | ---> WR DATA
* | RP | <--- RD DATA
* | BUS | <--- ACKNOWLEDGE
* /------\ \--------/
* RD ADDRESS ----> | RD | |
* RD DATA <---- | CH | -----------
* \------/
*
*
* Because AXI bus is quite complex simplier bus was created.
*
* It combines write and read channel, where write has bigger priority. Command
* is then send forward to red pitaya bus. When wite or read acknowledge is
* received AXI response is created and new AXI is accepted.
*
* To prevent AXI lockups because no response is received, this slave creates its
* own after 32 cycles (ack_cnt).
*
*/
module axi_slave
#(
parameter AXI_DW = 64 , // data width (8,16,...,1024)
parameter AXI_AW = 32 , // address width
parameter AXI_IW = 8 , // ID width
parameter AXI_SW = AXI_DW >> 3 // strobe width - 1 bit for every data byte
)
(
// global signals
input axi_clk_i , //!< AXI global clock
input axi_rstn_i , //!< AXI global reset
// axi write address channel
input [ AXI_IW-1: 0] axi_awid_i , //!< AXI write address ID
input [ AXI_AW-1: 0] axi_awaddr_i , //!< AXI write address
input [ 4-1: 0] axi_awlen_i , //!< AXI write burst length
input [ 3-1: 0] axi_awsize_i , //!< AXI write burst size
input [ 2-1: 0] axi_awburst_i , //!< AXI write burst type
input [ 2-1: 0] axi_awlock_i , //!< AXI write lock type
input [ 4-1: 0] axi_awcache_i , //!< AXI write cache type
input [ 3-1: 0] axi_awprot_i , //!< AXI write protection type
input axi_awvalid_i , //!< AXI write address valid
output axi_awready_o , //!< AXI write ready
// axi write data channel
input [ AXI_IW-1: 0] axi_wid_i , //!< AXI write data ID
input [ AXI_DW-1: 0] axi_wdata_i , //!< AXI write data
input [ AXI_SW-1: 0] axi_wstrb_i , //!< AXI write strobes
input axi_wlast_i , //!< AXI write last
input axi_wvalid_i , //!< AXI write valid
output axi_wready_o , //!< AXI write ready
// axi write response channel
output [ AXI_IW-1: 0] axi_bid_o , //!< AXI write response ID
output reg [ 2-1: 0] axi_bresp_o , //!< AXI write response
output reg axi_bvalid_o , //!< AXI write response valid
input axi_bready_i , //!< AXI write response ready
// axi read address channel
input [ AXI_IW-1: 0] axi_arid_i , //!< AXI read address ID
input [ AXI_AW-1: 0] axi_araddr_i , //!< AXI read address
input [ 4-1: 0] axi_arlen_i , //!< AXI read burst length
input [ 3-1: 0] axi_arsize_i , //!< AXI read burst size
input [ 2-1: 0] axi_arburst_i , //!< AXI read burst type
input [ 2-1: 0] axi_arlock_i , //!< AXI read lock type
input [ 4-1: 0] axi_arcache_i , //!< AXI read cache type
input [ 3-1: 0] axi_arprot_i , //!< AXI read protection type
input axi_arvalid_i , //!< AXI read address valid
output axi_arready_o , //!< AXI read address ready
// axi read data channel
output [ AXI_IW-1: 0] axi_rid_o , //!< AXI read response ID
output reg [ AXI_DW-1: 0] axi_rdata_o , //!< AXI read data
output reg [ 2-1: 0] axi_rresp_o , //!< AXI read response
output reg axi_rlast_o , //!< AXI read last
output reg axi_rvalid_o , //!< AXI read response valid
input axi_rready_i , //!< AXI read response ready
// RP system read/write channel
output [ AXI_AW-1: 0] sys_addr_o , //!< system bus read/write address.
output [ AXI_DW-1: 0] sys_wdata_o , //!< system bus write data.
output reg [ AXI_SW-1: 0] sys_sel_o , //!< system bus write byte select.
output reg sys_wen_o , //!< system bus write enable.
output reg sys_ren_o , //!< system bus read enable.
input [ AXI_DW-1: 0] sys_rdata_i , //!< system bus read data.
input sys_err_i , //!< system bus error indicator.
input sys_ack_i //!< system bus acknowledge signal.
);
//---------------------------------------------------------------------------------
//
// AXI slave Module
wire ack ;
reg [ 6-1: 0] ack_cnt ;
reg rd_do ;
reg [ AXI_IW-1: 0] rd_arid ;
reg [ AXI_AW-1: 0] rd_araddr ;
reg rd_error ;
wire rd_errorw ;
reg wr_do ;
reg [ AXI_IW-1: 0] wr_awid ;
reg [ AXI_AW-1: 0] wr_awaddr ;
reg [ AXI_IW-1: 0] wr_wid ;
reg [ AXI_DW-1: 0] wr_wdata ;
reg wr_error ;
wire wr_errorw ;
assign wr_errorw = (axi_awlen_i != 4'h0) || (axi_awsize_i != 3'b010); // error if write burst and more/less than 4B transfer
assign rd_errorw = (axi_arlen_i != 4'h0) || (axi_arsize_i != 3'b010); // error if read burst and more/less than 4B transfer
always @(posedge axi_clk_i) begin
if (axi_rstn_i == 1'b0) begin
rd_do <= 1'b0 ;
rd_error <= 1'b0 ;
end
else begin
if (axi_arvalid_i && !rd_do && !axi_awvalid_i && !wr_do) // accept just one read request - write has priority
rd_do <= 1'b1 ;
else if (axi_rready_i && rd_do && ack)
rd_do <= 1'b0 ;
if (axi_arvalid_i && axi_arready_o) begin // latch ID and address
rd_arid <= axi_arid_i ;
rd_araddr <= axi_araddr_i ;
rd_error <= rd_errorw ;
end
end
end
always @(posedge axi_clk_i) begin
if (axi_rstn_i == 1'b0) begin
wr_do <= 1'b0 ;
wr_error <= 1'b0 ;
end
else begin
if (axi_awvalid_i && !wr_do && !rd_do) // accept just one write request - if idle
wr_do <= 1'b1 ;
else if (axi_bready_i && wr_do && ack)
wr_do <= 1'b0 ;
if (axi_awvalid_i && axi_awready_o) begin // latch ID and address
wr_awid <= axi_awid_i ;
wr_awaddr <= axi_awaddr_i ;
wr_error <= wr_errorw ;
end
if (axi_wvalid_i && wr_do) begin // latch ID and write data
wr_wid <= axi_wid_i ;
wr_wdata <= axi_wdata_i ;
end
end
end
assign axi_awready_o = !wr_do && !rd_do ;
assign axi_wready_o = (wr_do && axi_wvalid_i) || (wr_errorw && axi_wvalid_i) ;
assign axi_bid_o = wr_awid ;
//assign axi_bresp_o = {wr_error,1'b0} ; // 2'b10 SLVERR
//assign axi_bvalid_o = (sys_wen_o && axi_bready_i) || (wr_error && axi_bready_i) ;
assign axi_arready_o = !rd_do && !wr_do && !axi_awvalid_i ;
assign axi_rid_o = rd_arid ;
//assign axi_rdata_o = sys_rdata_i ;
always @(posedge axi_clk_i) begin
if (axi_rstn_i == 1'b0) begin
axi_bvalid_o <= 1'b0 ;
axi_bresp_o <= 2'h0 ;
axi_rlast_o <= 1'b0 ;
axi_rvalid_o <= 1'b0 ;
axi_rresp_o <= 2'h0 ;
end
else begin
axi_bvalid_o <= wr_do && ack ;
axi_bresp_o <= {(wr_error || ack_cnt[5]),1'b0} ; // 2'b10 SLVERR 2'b00 OK
axi_rlast_o <= rd_do && ack ;
axi_rvalid_o <= rd_do && ack ;
axi_rresp_o <= {(rd_error || ack_cnt[5]),1'b0} ; // 2'b10 SLVERR 2'b00 OK
axi_rdata_o <= sys_rdata_i ;
end
end
// acknowledge protection
always @(posedge axi_clk_i) begin
if (axi_rstn_i == 1'b0) begin
ack_cnt <= 6'h0 ;
end
else begin
if ((axi_arvalid_i && axi_arready_o) || (axi_awvalid_i && axi_awready_o)) // rd || wr request
ack_cnt <= 6'h1 ;
else if (ack)
ack_cnt <= 6'h0 ;
else if (|ack_cnt)
ack_cnt <= ack_cnt + 6'h1 ;
end
end
assign ack = sys_ack_i || ack_cnt[5] || (rd_do && rd_errorw) || (wr_do && wr_errorw); // bus acknowledge or timeout or error
//------------------------------------------
// Simple slave interface
always @(posedge axi_clk_i) begin
if (axi_rstn_i == 1'b0) begin
sys_wen_o <= 1'b0 ;
sys_ren_o <= 1'b0 ;
sys_sel_o <= {AXI_SW{1'b0}} ;
end
else begin
sys_wen_o <= wr_do && axi_wvalid_i && !wr_errorw ;
sys_ren_o <= axi_arvalid_i && axi_arready_o && !rd_errorw ;
sys_sel_o <= {AXI_SW{1'b1}} ;
end
end
assign sys_addr_o = rd_do ? rd_araddr : wr_awaddr ;
assign sys_wdata_o = wr_wdata ;
endmodule
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