Can't resolve multiple constant drivers for net Quartus error - verilog

Question

this is a very basic question but if somebody can help me with these errors, I'd really appreciate it. I am an EE undergrad, new to Verilog, and I'd appreciate any help/explanation.
The errors I received were:
10028 Can't resolve multiple constant drivers for "led" at compare_block.sv (66)
10029 Constant driver at compare_block.sv(61)
What are the multiple constant drivers here? Originally, I had the led assignment (led <= led_val) within the second always block, and I thought moving it up to the first always block would change the errors, but it did not.
module compare_block (clk, reset_n, result, led);
parameter data_width = 8; /
parameter size = 1000;
input clk, reset_n;
input [data_width:0] result;
logic [(data_width):0] data_from_rom;
logic [9:0] addr_to_rom;
output reg led;
reg [(data_width):0] comp_sig [size-1:0];
reg [data_width:0] comp_sig_temp;
reg [(data_width):0] filt_sig [size-1:0];
reg [(data_width):0] ans_sig [size-1:0];
integer i, iii;
reg [9:0] ii ;
integer sum_array;
wire [(data_width+3):0] array_avg;
reg [data_width:0] summed_arr [size-2 : 0];//container for all summation steps
wire total_sum;
reg ans_sig_done;
reg [data_width : 0] summed_ans;
reg [data_width:0] max_val, error_val;
initial begin
i = 0;
ii = 0;
led=0;
data_from_rom='b000000000;
summed_ans='b000000000;
max_val='b000000000;
for (iii=0;iii<(size-1);iii=iii+1) begin
filt_sig[iii]=0;
ans_sig [iii]=0;
comp_sig[iii]=0;
summed_arr[iii]=0;
end
end
//port map to ROM
rom_compare ref_wave(
.clk(clk),
.addr(addr_to_rom), //text file?
.data(data_from_rom)
);
//Moore FSM
localparam [3:0]
s0=0, s1 = 1, s2 = 2, s3 = 3, s4 = 4, s5 = 5;
reg [3:0] state_reg, state_next;
initial state_next = 0;
always #(posedge clk, negedge reset_n) begin
if (reset_n == 'b0) begin //reset is active low
state_reg <= s0;
end else begin
state_reg <= state_next;
led <= led_val;
end
end
always #(state_reg) begin
state_next = state_reg;
led=0;
case (state_reg)
s0 : begin //initial state, reset state
if (!reset_n) begin
led <= 0;
ii <= 0;
end else begin
state_next <= s1;
end
end
s1 : begin
if (ii>(size)) begin
ii <= 0;
end else begin
addr_to_rom <= ii;
state_next <= s2;
end
end
s2 : begin
comp_sig_temp <= data_from_rom;
filt_sig [ii] <= result;
state_next <= s3;
end
s3 : begin
comp_sig[ii] <= comp_sig_temp;
state_next <= s4;
end
s4 : begin
ans_sig[ii] <= filt_sig[ii] - comp_sig[ii];
state_next <= s5;
end
s5 : begin
if (ii>(size-2)) begin
ans_sig_done = 1;
end else begin
ans_sig_done = 0;
end
ii <= ii+1;
state_next <= s0;
end
endcase
end
reg [(data_width+2):0] sum;
integer j;
always #* begin
sum = 0;
if (ans_sig_done == 1) begin
for (j=4; j<(size-1); j=j+2) begin
sum = sum +ans_sig[j];
if (ans_sig[j] > max_val) begin
max_val = ans_sig[j];
end
end
end
end
assign array_avg = sum >> 'd3; //2^3 = 8
always #(clk, result) begin //posedge clk, result
filt_sig [i] <= result;
i <= i + 1;
end
assign error_val = max_val >> 'd2; //approx 25% of max value of array
reg led_val;
always #(*)
begin
if (array_avg < error_val) begin
led_val <= 'b1;
end else begin
led_val <= 'b0;
end
end
endmodule

Answer 1

I figured it out!
The two instances were me trying to initialize one led = 0 in one always block and then assigning led <= led_val in another. You can't refer to an output in two different always blocks.