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URL https://opencores.org/ocsvn/t6507lp/t6507lp/trunk

Subversion Repositories t6507lp

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  • This comparison shows the changes necessary to convert path 
    /t6507lp/trunk/rtl/verilog
    from Rev 120 to Rev 119
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  •

Rev 120 → Rev 119

/t6507lp_fsm.v
10,7 → 10,6
//// ////
//// TODO: ////
//// - Fix relative mode, bit 7 means negative ////
//// - Check reset behavior ////
//// - Comment the code ////
//// ////
//// Author(s): ////
145,21 → 144,14
reg plp;
reg jsr;
 
wire [ADDR_SIZE_:0] next_pc; // a simple logic to add one to the PC
wire [ADDR_SIZE_:0] next_pc;
assign next_pc = pc + 13'b0000000000001;
 
wire [8:0] sp_plus_one; // simple adder and subtracter for the stack pointer
assign sp_plus_one = sp + 9'b000000001;
 
wire [8:0] sp_minus_one;
assign sp_minus_one = sp - 9'b000000001;
 
reg [ADDR_SIZE_:0] address_plus_index; // this two registers are used when the instruction uses indexing.
reg page_crossed; // address_plus_index always adds index to address and page_crossed asserts when the sum creates a carry.
reg [ADDR_SIZE_:0] address_plus_index; // this would update more times than actually needed, consuming power.
reg page_crossed; // so the simple assign was changed into a combinational always block
reg branch; // a simple reg that is asserted everytime a branch will be executed.
reg branch;
 
// this is the combinational logic related to indexed instructions
always @(*) begin
address_plus_index = 8'h00;
page_crossed = 1'b0;
171,7 → 163,7
else if (branch) begin
if (state == FETCH_OP_FIX_PC || state == FETCH_OP_EVAL_BRANCH) begin
{page_crossed, address_plus_index[7:0]} = pc[7:0] + index;
address_plus_index[12:8] = pc[12:8] + page_crossed; // warning: pc might feed these lines twice and cause branch failure
address_plus_index[12:8] = pc[12:8] + page_crossed;// warning: pc might feed these lines twice and cause branch failure
end // solution: add a temp reg i guess
end
else if (state == READ_FROM_POINTER) begin
198,6 → 190,12
end
end
 
wire [8:0] sp_plus_one;
assign sp_plus_one = sp + 9'b000000001;
 
wire [8:0] sp_minus_one;
assign sp_minus_one = sp - 9'b000000001;
 
always @ (posedge clk or negedge reset_n) begin // sequencial always block
if (reset_n == 1'b0) begin
// all registers must assume default values
208,7 → 206,7
temp_data <= 8'h00;
state <= RESET;
// registered outputs also receive default values
address <= 13'h0000;
address <= 0;
mem_rw <= MEM_READ;
data_out <= 8'h00;
end
232,7 → 230,7
end
/*
in this state the opcode is already known so truly execution begins.
all instructions execute this cycle.
all instruction execute this cycle.
*/
FETCH_LOW: begin
if (accumulator || implied) begin
370,7 → 368,6
end
end
end
// read memory at address
READ_MEM: begin
if (read_modify_write) begin
pc <= pc;
406,7 → 403,7
mem_rw <= MEM_READ;
data_out <= 8'h00;
 
if (page_crossed) begin // fix address
if (page_crossed) begin
address <= address_plus_index;
temp_addr <= address_plus_index;
end
429,7 → 426,6
temp_addr <= address_plus_index;
end
end
// some instructions have a dummy write cycle. this is it.
DUMMY_WRT_CALC: begin
pc <= pc;
address <= temp_addr;
572,7 → 568,7
end
end
 
always @ (*) begin // this is the next_state logic and the combinational output logic always block
always @ (*) begin // this is the next_state logic and the output logic always block
alu_opcode = 8'h00;
alu_a = 8'h00;
alu_enable = 1'b0;

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