16bit multiplier vhdl code synthesize error - vhdl

I want to write a 16bit * 16bit multiplication code. Here is my code:
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
entity mul is
port
(
A, B: IN INTEGER RANGE -32768 TO 32767;
C: OUT INTEGER RANGE -2147483648 TO +2147483647
);
end mul;
architecture Behavioral of mul is
begin
C <= A * B;
end behavioral;
But when I'm trying to sythesize the code on xilinx isim I get this error:
ERROR:Bitgen:342 - This design contains pins which have locations (LOC) that are
not user-assigned or I/O Standards (IOSTANDARD) that are not user-assigned.
This may cause I/O contention or incompatibility with the board power or
connectivity affecting performance, signal integrity or in extreme cases
cause damage to the device or the components to which it is connected. To
prevent this error, it is highly suggested to specify all pin locations and
I/O standards to avoid potential contention or conflicts and allow proper
bitstream creation. To demote this error to a warning and allow bitstream
creation with unspecified I/O location or standards, you may apply the
following bitgen switch: -g UnconstrainedPins:Allow
ERROR:Bitgen:157 - Bitgen will terminate because of the above errors.

All the ports defined in the entity should have a pin assignment defined using ucf file. If you are missing an ucf file, the tool will go ahead and place the pins by itself. This is clearly stated in the error message.
NET"A(0)" LOC ="AB16" | IOSTANDARD ="LVTTL";
NET"A(1)" LOC ="AB16" | IOSTANDARD ="LVTTL";
...
In your example, the width of A & B is 16 bits and C is 32 bits. So you need to assign correct pin location and IO standard for all of them.

Related

Vivado 2015.1 VHDL Input/ Output Violation

I am getting through the tutorial of Nexys 4 DDR and I am implementing a simple MUX
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
library UNISIM;
use UNISIM.VComponents.all;
-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;
-- Uncomment the following library declaration if instantiating
-- any Xilinx leaf cells in this code.
--library UNISIM;
--use UNISIM.VComponents.all;
entity lab1_2_1 is
Port ( SW0 : in STD_LOGIC;
SW1 : in STD_LOGIC;
SW2 : in STD_LOGIC;
LED0 : out STD_LOGIC);
end lab1_2_1;
architecture Behavioral of lab1_2_1 is
Signal SW2_bar : STD_LOGIC;
Signal SW0_int : STD_LOGIC;
Signal SW1_int : STD_LOGIC;
begin
SW2_bar <= not SW2;
SW0_int <= SW0 and SW2_bar;
SW1_int <= SW1 and SW2;
LED0 <= SW0_int or SW1_int;
end Behavioral;
When I get to the part of generating a bitstream, I get this critical warning
NSTD #1 Critical Warning 1 out of 1 logical ports use I/O standard (IOSTANDARD) value 'DEFAULT', instead of a user assigned specific value. This may cause I/O contention or incompatibility with the board power or connectivity affecting performance, signal integrity or in extreme cases cause damage to the device or the components to which it is connected. To correct this violation, specify all I/O standards. This design will fail to generate a bitstream unless all logical ports have a user specified I/O standard value defined. To allow bitstream creation with unspecified I/O standard values (not recommended), use this command: set_property SEVERITY {Warning} [get_drc_checks NSTD-1]. NOTE: When using the Vivado Runs infrastructure (e.g. launch_runs Tcl command), add this command to a .tcl file and add that file as a pre-hook for write_bitstream step for the implementation run. Problem ports: LED0.
and
UCIO #1 Critical Warning 1 out of 1 logical ports have no user assigned specific location constraint (LOC). This may cause I/O contention or incompatibility with the board power or connectivity affecting performance, signal integrity or in extreme cases cause damage to the device or the components to which it is connected. To correct this violation, specify all pin locations. This design will fail to generate a bitstream unless all logical ports have a user specified site LOC constraint defined. To allow bitstream creation with unspecified pin locations (not recommended), use this command: set_property SEVERITY {Warning} [get_drc_checks UCIO-1]. NOTE: When using the Vivado Runs infrastructure (e.g. launch_runs Tcl command), add this command to a .tcl file and add that file as a pre-hook for write_bitstream step for the implementation run. Problem ports: LED0.
Any Ideas?
Vivado expects you to define physical locations of the IOs and IO standards. IO standard depends on the voltage level and pull-up/pull-down resistors connected to pins of the FPGA.
You may add those into a constraint file (e.g. SDC or XDC). For example, I assigned output LED0 to pin A1 of the FPGA and defined the IO standard as 2.5V LVCMOS. The correct values can be found in the manual of your FPGA board.
set_property PACKAGE_PIN A1 [get_ports {LED0}];
set_property IOSTANDARD LVCMOS25 [get_ports {LED0}];

iCEstick + yosys - using the Global Set/Reset (GSR)

This is probably more of an iCEstick question than a yosys one, but asking here since I'm using the Icestorm tool chain.
I want to specify startup behavior of my design, which various places on the internet seem to agree is related to the typically named rst signal. It wasn't obvious to me where such a signal comes from, so I dug into the powerup sequence. Current understanding is from Figure 2 in this document.
After CDONE is pulled high by the device, all of the internal registers have been reset, to some initial value. Now, I've found plenty of lattice documents about how each type of flip-flop or hard IP receives a reset signal and does something with its internal state, but I still don't quite understand how I specify what those states are (or even just know what they are so I can use them).
For example, if I wanted to bring an LED high for 1 second after powerup (and only after powerup) I would want to start a counter after this reset signal (whatever it is) disables.
Poking around the ice40 family data sheet and the Lattice site, I found this document about using the Global Set/Reset signal. I confirmed this GSR is mentioned in the family data sheet, referenced on page 2-3 under "Clock/Control Distribution Network". It seems that a global reset signal is usable by one of the global buffers GBUF[0-7] and can be routed (up to 4 of them) to all LUTs with the global/high-fanout distribution network.
This seems like exactly what I was after, I but I can't find any other info about how to use this in my designs. The document on using the GSR states that you can instantiate a native GSR component like this:
GSR GSR_INST (.GSR (<global reset sig>));
but I can't tell whether this is just for simulation. Am I completely going in the wrong direction here or just missing something? I'm very inexperienced with FPGAs and hardware, so its entirely possible my entire approach is flawed.
I'm not sure if that GSR document actually is about iCE40. The Lattice iCEcube tool interestingly accepts instances of GSR cells, but it seems to simply treat them as constant zero drivers. There is also no simulation model for the GSR cell type in the iCE40 sim library and no description of it in the iCE40 tech library documentation provided by Lattice.
Furthermore, I have built the following two designs with the lattice tools, and besides the timestamp in the "comment field" of the generated bit-stream file, the generated bit-streams are identical! (This test was performed with Lattice LSE as synthesis tool, not Synplify. I had problems getting Synplify to run on my machine for some reason and gave up trying to do so over a year ago..)
This is the first test design I've used:
module top (
input clk,
output rst,
output reg val
);
always #(posedge clk, posedge rst)
if (rst)
val = 1;
else
val = 0;
GSR GSR_INST (.GSR (rst));
endmodule
And this is the second test design:
module top (
input clk,
output rst,
output val
);
assign val = 0, rst = 0;
endmodule
Given this results I think it is safe to say that the lattice tools simply ignore GSR cells in iCE40 designs. (Maybe for compatibility with their other FPGA families?)
So how does one generate a rst signal then? For example, the following is a simple reset generator that asserts (pulls low) resetn for the first 15 cycles:
input clk;
...
wire resetn;
reg [3:0] rststate = 0;
assign resetn = &rststate;
always #(posedge clk) rststate <= rststate + !resetn;
(The IceStorm flow does support arbitrary initialization values for registers, whereas the lattice tools ignore the initialization value and simply initialize all FFs to zero. So if you want your designs to be portable between the tools, it is recommended to only initialize regs to zero.)
If you are using a PLL, then it is custom to use the PLL LOCK output to drive the resetn signal. Unfortunately the "iCE40 sysCLOCK PLL Design and Usage Guide" does not state if the generated LOCK signal is already synchronous to the generated clock, so it would be a good idea to synchronize it to the clock to avoid problems with metastability:
wire clk, resetn, PLL_LOCKED;
reg [3:0] PLL_LOCKED_BUF;
...
SB_PLL40_PAD #( ... ) PLL_INST (
...
.PLLOUTGLOBAL(clk),
.LOCK(PLL_LOCKED)
);
always #(posedge clk)
PLL_LOCKED_BUF <= {PLL_LOCKED_BUF, PLL_LOCKED};
assign resetn = PLL_LOCKED_BUF[3];
Regarding usage of global nets: You can explicitly route the resetn signal via a global net (using the SB_GB primitive), but using the IceStorm flow, arachne-pnr will automatically route a set/reset signal (when used by more than just a few FFs) over a global net, if a global net is available.

XILINX ISE set I/O Marker as Clock

I'm on Xilinx ISE IDE and using the Schematic Editor.
(click for new window)
The constraints file is following:
NET "A" LOC = M18;
NET "F" LOC = P15;
NET "B" LOC = M16;
NET "A" PULLUP;
NET "B" PULLUP;
NET "F" DRIVE = 8;
But when I want to compile my program, there is this error:
ERROR:Place:1108 - A clock IOB / BUFGMUX clock component pair have been found
that are not placed at an optimal clock IOB / BUFGMUX site pair. The clock
IOB component <B> is placed at site <M16>. The corresponding BUFG component
<B_BUFGP/BUFG> is placed at site <BUFGMUX_X2Y3>. There is only a select set
of IOBs that can use the fast path to the Clocker buffer, and they are not
being used. You may want to analyze why this problem exists and correct it.
If this sub optimal condition is acceptable for this design, you may use the
CLOCK_DEDICATED_ROUTE constraint in the .ucf file to demote this message to a
WARNING and allow your design to continue. However, the use of this override
is highly discouraged as it may lead to very poor timing results. It is
recommended that this error condition be corrected in the design. A list of
all the COMP.PINs used in this clock placement rule is listed below. These
examples can be used directly in the .ucf file to override this clock rule.
< NET "B" CLOCK_DEDICATED_ROUTE = FALSE; >
ERROR:Pack:1654 - The timing-driven placement phase encountered an error.
How to fix it?
While any signal can theoretically be used as a clock, it's not true for FPGA; at least not optimally. Clocks need special considerations that translate to restriction on which pin of the FPGA can be routed to the clock network.
I suspect that in your case, you used a push-button to act as a clock signal, which will only work on a very small design (like yours) because of debouncing and the fact that it's not a clock-enabled input port.
You can tell the tool that you want the sub-optimal and potentially erroneous clock path by adding the following constraint to your .ucf:
NET "B" CLOCK_DEDICATED_ROUTE = FALSE;
Keep in mind that you shouldn't do that without being sure that your design is fine with it... I recommend that you do further design with a "real" clock connected to a clock port on your FPGA, every board has one. That constraint will make your design work, but in a larger, faster design is likely to be a source of problems.

how does inout parameters be implemented?

I know what the inout parameters is and how to use them. Assume that we have an inout parameter io and want to create a bidirectional static RAM such as the following code :
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY sram IS
port(
clk : IN std_logic;
wr : IN std_logic;
io : INOUT std_logic;
addr : IN INTEGER RANGE 0 TO 7
);
END sram;
ARCHITECTURE behavioral OF sram IS
TYPE matrix IS ARRAY (0 TO 7) OF std_logic;
SIGNAL mem : matrix;
BEGIN
PROCESS(clk)
BEGIN
IF rising_edge(clk) THEN
IF wr = '1' THEN
mem(addr) <= io;
END IF;
END IF;
END PROCESS;
io <= mem(addr) WHEN wr = '0' ELSE 'Z';
END behavioral;
We can create an instance of sram and write on it such as the following code :
io <= '1' WHEN wr = '1' ELSE 'Z';
Question : How can synthesis tool control the multiple assignments and judge between multiple drivers ? What hardware is implemented to do it ?
Thanks for comments and answers ...
For typical FPGA and ASIC devices, implementation of tristate capabilities are only available on the IO, like for example in an Altera Arria 10 FPGA:
So for such devices, the internal RAMs are always implemented with dedicated input and output ports, thus not using any internal tristate capabilities.
Even if a RAM is connected to external IOs that support tristate, then the internal RAM block is still typically created with dedicated input and output ports, so the connection to a tristate capable pin on the device is handled through an in-out buffer with the output enable and tristate capability.
If internal design tries to use tristate capabilities or multiple drivers when this is not supported by the device, then the synthesis tool will generate and error, typically saying that multiple drivers are not supported for the same net.
On Xilinx devices, the schematics are similar.
This is an image of primitive IOBUF:
The green part is the output driver with tristate control; the blue part is the input driver. The complete IOB (Input/Output Block) consists of several primitives:
IOB registers (input, output, tristate control)
delay chains
wires to combine two IOBs to a differential IOB (**BUFDS)
capability to drive clock networks (CC-IOB - clock capable IOB)
pullup, pulldown, ...
driver (IOBUF)
pin/ball (IPAD, OPAD, IOPAD) - this includes ESD protection
How does synthesis work?
Xilinx synthesis tools (XST / Synth) add IPAD or OPAD primitives for every wire in your top-level component's port description. A pad is just the primitive to represent a physical pin or ball under the FPGA package.
If you enabled to automatically add I/O buffers, the tool will add IBUF, OBUF, IOBUF, IBUFDS, ... primitives between every PAD and top-level port. It uses the port direction (in, out, inout) to infer the correct buffer type. If this option is disabled (default = on) you have to manually add buffers for every I/O pin. In some cases XST gets offended: I added some IOBUFs with tristate control by hand so XST declined to infer the missing buffers. So I had to add all buffers by hand ...
While using Xilinx XST it's possible to use tristate buses (port direction = inout) beneath the top-level. XST will report that it added (virtual) tristate buffers. These buffers get trimmed if the direction of each bit of the bus has an obvious direction and no multiple driver problem.
This does not work in iSim.

Inferred RAM doesn't initialize in ModelSim Altera edition

I have a memory module for an Altera FPGA target that I've written to be inferred into one of Altera's ALTSYNCRAM blocks. The memory is 1024x16 and I have a memory initialization file specified with an attribute.
When synthesizing, the synthesis report indicates that it generated the type of RAM block that I wanted, and it notes that the initialization file is the one I specified.
When trying to simulate with Altera's edition of ModelSim, the data signal starts out completely uninitialized, and I can't figure out why.
I looked on forums and such and some people mentioned that ModelSim might not support the ".mif" format that I was using, but would support ".hex" so I changed my initialization file to ".hex". I also read that relative file paths can be an issue, but I checked my simulation directory and it looks like QuartusII copied the initialization file into that directory when I tried to simulate.
Any ideas on why the memory isn't being initialized and how to make it do so?
A heavily trimmed model that contains the inferred memory:
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library work;
--use work.types.all;
entity CPU is
--...
end entity CPU;
architecture rtl of CPU is
--these types are actually included in a package
subtype reg is std_logic_vector(15 downto 0);
type mem is array (0 to 1023) of reg;
--...
--memory read port
signal MR : reg;
signal MRA : std_logic_vector(9 downto 0); --flops
--memory write port
signal MW : reg; --flops
signal MWA : std_logic_vector(9 downto 0); --flops
signal MWE : std_logic; --flop
signal data : mem;
attribute ram_init_file : string;
attribute ram_init_file of data : signal is "RAM_init.hex";
attribute ramstyle : string;
attribute ramstyle of data : signal is "no_rw_check";
begin
--...
--memory spec
MR <= data(to_integer(unsigned(MRA(9 downto 0))));
memory_process : process(clk)
begin
if (clk'event and clk = '1') then
if(MWE = '1') then
data(to_integer(unsigned(MWA(9 downto 0)))) <= MW;
end if;
end if;
end process;
end architecture rtl; --CPU
Modelsim does not show any warnings or errors while compiling CPU.vhd, nor does it have any indication of loading the initialization file.
This is my first design using Altera software or memory initialization files, and it wouldn't surprise me if the problem was something really basic, or I'm approaching this from a fundamentally incorrect angle.
I'd normally define the memory with a constant in a package, but this is for a class, and it requires that I have a memory initialization file (it requires .mif format too, but that's only a 3 character change between simulation and synthesis file).
It looks like Modelsim may have a "mem load" command you can use at the start of your simulation in order to initialize the memory. Take a look at the end of this thread:
Initialization altsyncram
Being able to initialize RAM on an FPGA depends on both the synthesizer and the specific FPGA you are using. Some FPGA families support this, others don't. I know this is not the answer you want to hear, but you'll need to check the documentation from Altera.
Modelsim does not pay attention to synthesis attributes. That is a vendor specific convention. You can refer to them in simulation as with any other user-defined attribute but it doesn't know that some attributes invoke special behavior in various third-party synthesizers.
If you want to initialize the RAM for simulation you will need to do one of the following:
Write a function that reads the contents of the memory file and call it during initialization of the data signal.
Convert the memory contents to a VHDL constant defined in a separate package and assign the constant to the data signal as the initializer. This can be automated with a script.
Use the Verilog system task $readmemh (requires Modelsim with mixed language license)
For option 1, the function should be of the form:
impure function read_mem(fname : string) return mem is
variable data : mem;
begin
-- ** Perform read with textio **
...
return data;
end function;
signal data : mem := read_mem(data'ram_init_file);
The Quartus documentation on RAM initialization is sparse and only demonstrates initialized data assigned from within a VHDL process rather than reading from a file. The Xilinx documentation on RAM/ROM inferencing (p258) provides examples for doing this with general purpose VHDL. The same technique can be used for simulating a design targeted to Altera. XST supports this use of file I/O for synthesis but Quartus may choke on it. If that is the case you will have to use a configuration to swap between a synthesis oriented RAM model and one specifically for simulation that initializes with the function.
The Xilinx example only shows how to read files with ASCII binary. I have a general purpose ROM component that reads hex as well as binary which you can adapt into a RAM for what you need.

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