| //------------------------------------------------------ |
| // caravel_spi_slave.v |
| //------------------------------------------------------ |
| // General purpose SPI slave module for the Caravel chip |
| //------------------------------------------------------ |
| // Written by Tim Edwards |
| // efabless, inc., September 28, 2020 |
| //------------------------------------------------ |
| // This file is distributed free and open source |
| //------------------------------------------------ |
| |
| // SCK --- Clock input |
| // SDI --- Data input |
| // SDO --- Data output |
| // CSB --- Chip select (sense negative) |
| // idata --- Data from chip to transmit out, in 8 bits |
| // odata --- Input data to chip, in 8 bits |
| // addr --- Decoded address to upstream circuits |
| // rdstb --- Read strobe, tells upstream circuit to supply next byte to idata |
| // wrstb --- Write strobe, tells upstream circuit to latch odata. |
| |
| // Data format (general purpose): |
| // 8 bit format |
| // 1st byte: Command word (see below) |
| // 2nd byte: Address word (register 0 to 255) |
| // 3rd byte: Data word (value 0 to 255) |
| |
| // Command format: |
| // 00000000 No operation |
| // 10000000 Write until CSB raised |
| // 01000000 Read until CSB raised |
| // 11000000 Simultaneous read/write until CSB raised |
| // 11000100 Pass-through read/write to management area flash SPI until CSB raised |
| // 11000101 Pass-through read/write to user area flash SPI until CSB raised |
| // wrnnn000 Read/write as above, for nnn = 1 to 7 bytes, then terminate |
| |
| // Lower three bits are reserved for future use. |
| // All serial bytes are read and written msb first. |
| |
| // Fixed control and status registers |
| |
| // Address 0 is reserved and contains flags for SPI mode. This is |
| // currently undefined and is always value 0. |
| // Address 1 is reserved and contains manufacturer ID low 8 bits. |
| // Address 2 is reserved and contains manufacturer ID high 4 bits. |
| // Address 3 is reserved and contains product ID (8 bits). |
| // Addresses 4 to 7 are reserved and contain the mask ID (32 bits). |
| // Addresses 8 to 255 are available for general purpose use. |
| |
| `define COMMAND 3'b000 |
| `define ADDRESS 3'b001 |
| `define DATA 3'b010 |
| `define USERPASS 3'b100 |
| `define MGMTPASS 3'b101 |
| |
| module caravel_spi_slave(reset, SCK, SDI, CSB, SDO, |
| sdoenb, idata, odata, oaddr, rdstb, wrstb, |
| pass_thru_mgmt, pass_thru_mgmt_delay, |
| pass_thru_user, pass_thru_user_delay, pass_thru_reset); |
| |
| input reset; |
| input SCK; |
| input SDI; |
| input CSB; |
| output SDO; |
| output sdoenb; |
| input [7:0] idata; |
| output [7:0] odata; |
| output [7:0] oaddr; |
| output rdstb; |
| output wrstb; |
| output pass_thru_mgmt; |
| output pass_thru_mgmt_delay; |
| output pass_thru_user; |
| output pass_thru_user_delay; |
| output pass_thru_reset; |
| |
| reg [7:0] addr; |
| reg wrstb; |
| reg rdstb; |
| reg sdoenb; |
| reg [2:0] state; |
| reg [2:0] count; |
| reg writemode; |
| reg readmode; |
| reg [2:0] fixed; |
| wire [7:0] odata; |
| reg [6:0] predata; |
| wire [7:0] oaddr; |
| reg [7:0] ldata; |
| reg pass_thru_mgmt; |
| reg pass_thru_mgmt_delay; |
| reg pre_pass_thru_mgmt; |
| reg pass_thru_user; |
| reg pass_thru_user_delay; |
| reg pre_pass_thru_user; |
| wire csb_reset; |
| |
| assign odata = {predata, SDI}; |
| assign oaddr = (state == `ADDRESS) ? {addr[6:0], SDI} : addr; |
| assign SDO = ldata[7]; |
| assign csb_reset = CSB | reset; |
| assign pass_thru_reset = pass_thru_mgmt_delay | pre_pass_thru_mgmt; |
| |
| // Readback data is captured on the falling edge of SCK so that |
| // it is guaranteed valid at the next rising edge. |
| always @(negedge SCK or posedge CSB) begin |
| if (CSB == 1'b1) begin |
| wrstb <= 1'b0; |
| ldata <= 8'b00000000; |
| sdoenb <= 1'b1; |
| end else begin |
| |
| // After CSB low, 1st SCK starts command |
| |
| if (state == `DATA) begin |
| if (readmode == 1'b1) begin |
| sdoenb <= 1'b0; |
| if (count == 3'b000) begin |
| ldata <= idata; |
| end else begin |
| ldata <= {ldata[6:0], 1'b0}; // Shift out |
| end |
| end else begin |
| sdoenb <= 1'b1; |
| end |
| |
| // Apply write strobe on SCK negative edge on the next-to-last |
| // data bit so that it updates data on the rising edge of SCK |
| // on the last data bit. |
| |
| if (count == 3'b111) begin |
| if (writemode == 1'b1) begin |
| wrstb <= 1'b1; |
| end |
| end else begin |
| wrstb <= 1'b0; |
| end |
| end else if (state == `MGMTPASS || state == `USERPASS) begin |
| wrstb <= 1'b0; |
| sdoenb <= 1'b0; |
| end else begin |
| wrstb <= 1'b0; |
| sdoenb <= 1'b1; |
| end // ! state `DATA |
| end // ! CSB |
| end // always @ ~SCK |
| |
| always @(posedge SCK or posedge CSB) begin |
| if (csb_reset == 1'b1) begin |
| // Default state on reset |
| addr <= 8'h00; |
| rdstb <= 1'b0; |
| predata <= 7'b0000000; |
| state <= `COMMAND; |
| count <= 3'b000; |
| readmode <= 1'b0; |
| writemode <= 1'b0; |
| fixed <= 3'b000; |
| pass_thru_mgmt <= 1'b0; |
| pass_thru_mgmt_delay <= 1'b0; |
| pre_pass_thru_mgmt <= 1'b0; |
| pass_thru_user = 1'b0; |
| pass_thru_user_delay <= 1'b0; |
| pre_pass_thru_user <= 1'b0; |
| end else begin |
| // After CSB low, 1st SCK starts command |
| if (state == `COMMAND) begin |
| rdstb <= 1'b0; |
| count <= count + 1; |
| if (count == 3'b000) begin |
| writemode <= SDI; |
| end else if (count == 3'b001) begin |
| readmode <= SDI; |
| end else if (count < 3'b101) begin |
| fixed <= {fixed[1:0], SDI}; |
| end else if (count < 3'b110) begin |
| pass_thru_mgmt_delay <= pre_pass_thru_mgmt; |
| pass_thru_user_delay <= pre_pass_thru_user; |
| end else if (count == 3'b111) begin |
| if (pre_pass_thru_mgmt == 1'b1) begin |
| state <= `MGMTPASS; |
| pre_pass_thru_mgmt <= 1'b0; |
| end else if (pre_pass_thru_user == 1'b1) begin |
| state <= `USERPASS; |
| pre_pass_thru_user <= 1'b0; |
| end else begin |
| state <= `ADDRESS; |
| end |
| end |
| end else if (state == `ADDRESS) begin |
| count <= count + 1; |
| addr <= {addr[6:0], SDI}; |
| if (count == 3'b111) begin |
| if (readmode == 1'b1) begin |
| rdstb <= 1'b1; |
| end |
| state <= `DATA; |
| end else begin |
| rdstb <= 1'b0; |
| end |
| end else if (state == `DATA) begin |
| predata <= {predata[6:0], SDI}; |
| count <= count + 1; |
| if (count == 3'b111) begin |
| if (fixed == 3'b001) begin |
| state <= `COMMAND; |
| end else if (fixed != 3'b000) begin |
| fixed <= fixed - 1; |
| addr <= addr + 1; // Auto increment address (fixed) |
| end else begin |
| addr <= addr + 1; // Auto increment address (streaming) |
| end |
| end else begin |
| rdstb <= 1'b0; |
| end |
| end // ! state `DATA |
| end // ! CSB |
| end // always @ SCK |
| |
| endmodule // caravel_spi_slave |
