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|
`include "core/uarch.sv"
module core_cycles
(
input logic clk,
dec_execute,
dec_branch,
dec_writeback,
dec_update_flags,
input ptr dec_branch_offset,
input data_decode dec_data,
input ptr fetch_insn_pc,
input psr_flags next_flags,
input word rd_value_b,
q_alu,
q_shifter,
input logic c_shifter,
output logic stall,
branch,
writeback,
update_flags,
c_in,
output reg_num rd,
ra,
rb,
output ptr branch_target,
pc_visible,
output psr_mode reg_mode,
output alu_op alu,
output word alu_b,
wr_value,
output shifter_control shifter,
output logic[7:0] shifter_shift
);
enum
{
EXECUTE,
RD_INDIRECT_SHIFT,
WITH_SHIFT
} cycle, next_cycle;
logic bubble, final_writeback, data_snd_is_imm, data_snd_shift_by_reg, trivial_shift;
logic[5:0] data_shift_imm;
logic[7:0] data_imm;
word saved_base;
reg_num r_shift, final_rd;
ptr pc;
assign stall = (next_cycle != EXECUTE) | bubble;
assign pc_visible = pc + 2;
assign reg_mode = `MODE_SVC; //TODO
always_comb begin
unique case(cycle)
RD_INDIRECT_SHIFT: shifter_shift = rd_value_b[7:0];
default: shifter_shift = {2'b00, data_shift_imm};
endcase
trivial_shift = 1;
if(final_writeback & (shifter.shl | shifter.shr | shifter.ror))
trivial_shift = shifter_shift == 0;
next_cycle = EXECUTE;
unique case(cycle)
EXECUTE:
if(data_snd_shift_by_reg)
next_cycle = RD_INDIRECT_SHIFT;
else if(~trivial_shift)
next_cycle = WITH_SHIFT;
RD_INDIRECT_SHIFT:
if(~trivial_shift)
next_cycle = WITH_SHIFT;
default: ;
endcase
if(bubble)
next_cycle = EXECUTE;
unique case(cycle)
EXECUTE:
if(data_snd_is_imm)
alu_b = {{24{1'b0}}, data_imm};
else
alu_b = rd_value_b;
RD_INDIRECT_SHIFT, WITH_SHIFT:
alu_b = saved_base;
endcase
end
always_ff @(posedge clk) begin
cycle <= next_cycle;
bubble <= 0;
writeback <= 0;
wr_value <= q_alu;
unique case(next_cycle)
EXECUTE: begin
branch <= 0;
update_flags <= 0;
branch_target <= {30{1'bx}};
final_writeback <= 0;
if(dec_execute & ~bubble) begin
bubble <=
(dec_update_flags & update_flags)
| (final_writeback & ((rd == dec_data.rn) | (rd == dec_data.r_snd)));
branch <= dec_branch;
update_flags <= dec_update_flags;
branch_target <= pc_visible + dec_branch_offset;
data_snd_is_imm <= dec_data.snd_is_imm;
data_snd_shift_by_reg <= dec_data.snd_shift_by_reg;
data_imm <= dec_data.imm;
data_shift_imm <= dec_data.shift_imm;
alu <= dec_data.op;
shifter.shl <= dec_data.shl;
shifter.shr <= dec_data.shr;
shifter.ror <= dec_data.ror;
shifter.put_carry <= dec_data.put_carry;
shifter.sign_extend <= dec_data.sign_extend;
ra <= dec_data.rn;
rb <= dec_data.r_snd;
r_shift <= dec_data.r_shift;
c_in <= next_flags.c;
final_rd <= dec_data.rd;
final_writeback <= dec_writeback;
end
writeback <= final_writeback;
rd <= final_rd;
pc <= fetch_insn_pc;
end
RD_INDIRECT_SHIFT: begin
rb <= r_shift;
data_snd_shift_by_reg <= 0;
saved_base <= rd_value_b;
end
WITH_SHIFT: begin
c_in <= c_shifter;
saved_base <= q_shifter;
end
endcase
end
initial begin
cycle = EXECUTE;
bubble = 0;
pc = 0;
c_in = 0;
branch = 1;
writeback = 0;
branch_target = 30'd0;
data_snd_shift_by_reg = 0;
final_rd = 0;
final_writeback = 0;
end
endmodule
|
