serv

/*
 * serv_aligner.v : Realign a misaligned 32-bit word fetched from memory
 *
 * SPDX-FileCopyrightText: 2022 Olof Kindgren <olof@award-winning.me>
 * SPDX-License-Identifier: ISC
 */
module serv_aligner
   (
    input wire clk,
    input wire rst,
    // serv_top
    input  wire [31:0]  i_ibus_adr,
    input  wire         i_ibus_cyc,
    output wire [31:0]  o_ibus_rdt,
    output wire         o_ibus_ack,
    // serv_rf_top
    output wire [31:0]  o_wb_ibus_adr,
    output wire         o_wb_ibus_cyc,
    input  wire [31:0]  i_wb_ibus_rdt,
    input  wire         i_wb_ibus_ack);

    wire [31:0] ibus_rdt_concat;
    wire        ack_en;

    reg  [15:0] lower_hw;
    reg         ctrl_misal ;

    /* From SERV core to Memory

    o_wb_ibus_adr: Carries address of instruction to memory. In case of misaligned access,
    which is caused by pc+2 due to compressed instruction, next instruction is fetched
    by pc+4 and concatenation is done to make the instruction aligned.

    o_wb_ibus_cyc: Simply forwarded from SERV to Memory and is only altered by memory or SERV core.
    */
    assign o_wb_ibus_adr = ctrl_misal ? (i_ibus_adr+32'b100) : i_ibus_adr;
    assign o_wb_ibus_cyc = i_ibus_cyc;

    /* From Memory to SERV core

        o_ibus_ack: Instruction bus acknowledge is send to SERV only when the aligned instruction,
        either compressed or un-compressed, is ready to dispatch.

        o_ibus_rdt: Carries the instruction from memory to SERV core. It can be either aligned
        instruction coming from memory or made aligned by two bus transactions and concatenation.
    */
    assign o_ibus_ack = i_wb_ibus_ack & ack_en;
    assign o_ibus_rdt = ctrl_misal ? ibus_rdt_concat : i_wb_ibus_rdt;

    /* 16-bit register used to hold the upper half word of the current instruction in-case
       concatenation will be required with the upper half word of upcoming instruction
    */
    always @(posedge clk) begin
        if(i_wb_ibus_ack)begin
            lower_hw <= i_wb_ibus_rdt[31:16];
        end
    end

    assign ibus_rdt_concat = {i_wb_ibus_rdt[15:0],lower_hw};

    /* Two control signals: ack_en, ctrl_misal are set to control the bus transactions between
    SERV core and the memory
    */
    assign ack_en   = !(i_ibus_adr[1] & !ctrl_misal);

    always @(posedge clk ) begin
        if(rst)
            ctrl_misal <= 0;
        else if(i_wb_ibus_ack & i_ibus_adr[1])
            ctrl_misal <= !ctrl_misal;
    end

endmodule