Application Notes

Moku Cloud Compile

A Getting Started Guide

Moku Cloud Compile is an innovative new feature available on Moku:Pro. The Moku family of test and measurement tools are FPGA based instruments and Moku Cloud Compile allows users to deploy custom VHDL code to a Moku. This code can provide custom features and interact with the existing instruments to unlock new and unique instrumentation only possible due the Moku’s Instrument-on-Chip architecture.

This tutorial will guide users from the very start of creating a Cloud Compile account through to coding and deployment of some simple VHDL examples. By the end of this guide, users will have the fundamental knowledge to compile and deploy custom code to Moku:Pro.

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Prerequisites

Moku:Pro with

Multi-Instrument Mode (MiM)

 Moku Cloud Compile (MCC)

If your Moku:Pro does not have MiM or MCC, please contact Liquid Instruments at [email protected] to enquire about evaluations and upgrades.

Overview

Liquid Instruments’ Cloud Compile tool enables users to design customer code and features for implementation on the Moku:Pro platform. Compared to CPI and application specific integrated circuits (ASIC) based DSP approaches,  FPGA platforms provide near ASIC-level latency and performance with being software programmable more like a traditional CPU.

While there are many software languages that can be employed to write software for CPU based designs, and these languages are widely taught and used; FPGA programming is limited to VHDL or Verilog and these have a steep learning curve and the tools are typically costly. Also, the platforms available for deploying VHDL code are limited to evaluation boards from FPGA vendors or a variety of limited functionality, open source hardware boards.

Moku:Pro combined with Moku Cloud Compile address the need for a high performance laboratory instrument with research grade hardware, combined with the ability to deploy custom VHDL without the overhead of a large suite of HDL compile, synthesize and route software.  MCC compiles the users’ customer VHDL in the cloud and delivers a bitstream over the internet, ready to deploy to any MCC enabled Moku:Pro

Multi-instrument mode and Cloud Compile

Moku:Pro Multi-instrument Mode (MiM) allows multiple instruments to be deployed and operate simultaneously. At the highest level; MiM presents 4 slots representing 4 partitions of the FPGA. Users can deploy a flexible arrangement of instruments into these slots. Figure 1 shows the MiM interface, with an


Figure 1: building a MiM system

oscilloscope deployed in slot 1, a spectrum analyzer deployed in slot 2 while slots 3 and 4 remain to be filled. The available instruments are: PID controller, Oscilloscope, Spectrum Analyzer, Lock-in Amplifier, Waveform Generator, Frequency Response Analyzer, Arbitrary Waveform Generator and Cloud Compile.

It is the Cloud Compile instrument, which here occupies slot 4 in Figure 2 into which we can deploy the user’s compiled VHDL code. MiM thus enables users’ VHDL to interact with the Moku instruments.


Figure 2: MiM built with Cloud Compile slot

Setting up a Cloud Compile account

Before we can compile or deploy code to a Moku, we need an online account. This is a simple process:

  • Setup a MCC user account at:  compile.liquidinstruments.com
  • First time users will need to select “Sign up”
    • Existing new users can login by username or email address, then entering their password
  • The Sign up page requires only a user-selected username, valid email address and user defined password.
  • Once signed up and logged in, you will see the Projects page, which initially will be empty, see Figure 3.


Figure 3: new project menu

  • Before our first VHDL example, we will configure the devices; select the Devices tab and configure as shown in Figure 4. choose a convenient name and then select Hardware version, Firmware version and No. of slots as shown.


Figure 4: configure new Moku device

VHDL example #1: routing inputs to outputs

Enter the VHDL code

Now that your Cloud Compile account is setup and you are familiar with the interface, we will write, compile and deploy the most basic instrument. Our very basic first instrument will simply take the Cloud Compiler slots’ input signals and connect them to the outputs.

Output A = InputA

OutputB = InputB

 

 

architecture Behavioural of CustomWrapper is
begin
     OutputA <= InputA;
     OutputB <= InputB;
end architecture;

Figure 5: full code for example #1; Input2Outputs.vhdl

Select ‘new project’ and assign it an appropriate name, here “Inputs2Outputs”.

The code for this first example is shown in Figure 5. This code defines the architecture of the entity ‘CustomWrapper’. ‘CustomerWrapper’ is the definition that provides the basic I/O definitions of our custom MCC instrument and the logic of it.

Within this project, “Inputs2Outputs” select the editor, create a new file named “Inputs2Outputs.vhdl”, this should look like Figure 6


Figure 6: new file in editor

Enter the text of figure 5. It should look like Figure 7.


Figure 7: VHDL code in editor

Build the code

Select the ‘Target device’, ‘Save’ and then ‘Build’. The code will then be submitted to the Cloud Compile server and you can select the Build tab to observe the process. This will take several minutes to complete.


Figure 8: Build underway

Once the code compilation is complete, the “Synthesize”, “Route”, Report” and “Bitstream” should all be green.  At the very bottom of this screen is the bitstream, or artifact, ‘bitstream.tar.gz’. Do not unzip or untar this bit stream.

It is likely you will see many compiler or synthesizer warnings; these can mostly be disregarded for our purpose.  However, any errors would need attention, errors are likely to halt the build process.


Figure 9: Successful build

Deploy the code

Now using the Moku iPad app, select MiM and then configure the slots and I/O as shown in Figure 10. This will prepare the Moku:Pro for the CC bitstream.


Figure 10: MiM slot configuration for example 1

The file “bitstream.tar.gz” can then be download to your local PC by clicking on the small download icon. We now have a final step to deploy the code to your Moku

  • Find IP address
    • In the iPad Moku app; touch and hold the Moku icon; this will reveal its IP address
  • Connect to your Moku
    • In a web browser, go to your Moku’s IP address

You should see the Moku:Pro web interface as shown in Figure 11.


Figure 11: Moku web browser interface

Next, choose the ‘bitstream.tar.gz’ that was downloaded earlier and upload it.  In this example, set slot 3 to ‘custom’, tick ‘force’ and select deploy. The custom code will be deployed to the Moku.

To provide a test of our new CC custom instrument, we deploy the slot 2 waveform generator with a 10 MHz sine wave on output 1 and a 1 MHz ramp wave on output 2. This then passes through our simple CC instrument that and by deploying the oscilloscope in slot 4,  these signals can be observed to confirm the correct ‘pass through’ operation of the slot 3 CC instrument.


Figure 12: a slot 2 waveform generator setup


Figure 13: slot 4 oscilloscope confirm CC operation

VHDL example #2: subtracting/adding inputs

Example 1 illustrated in great detail the steps required to compile and deploy a very simple VHDL example.

architecture Behavioural of CustomWrapper is
begin
     OutputA <= InputA + InputB;
     OutputB <= InputB - InputB;
end architecture;

Example 2 shows the VHDL to add and subtract inputs. While this is also a basic and example; it has many practical scenarios in the test and measurement world.

Users are encouraged to take this example and repeat the compile and deploy steps outlined in example #1. Verification might consist of using MiM with a Waveform Generator in slot 1; Cloud Compile in slot 2 and finally an oscilloscope in slot 3.  Visual confirm of correct operation might consist of adding and subtracting sine wave that are alternatively in phase and 180 degrees out of phase.

VHDL example #3: scaling and offset inputs / DSP slice

This example is slightly more complex than the first two examples.

use WORK.MercurySupport.ScaleOffset;

architecture Behavioural of CustomWrapper is
begin
    -- Z = X * Scale + Offset
    -- Clips Z to min/max (prevents over/underflow)
    -- Includes rounding
    -- One Clock Cycle Delay
    DSP: ScaleOffset
        port map (
            Clk => Clk,
            Reset => Reset,
            X => InputA,
            Scale => signed(Control1(15 downto 0)),
            Offset => signed(Control2(15 downto 0)),
            Z => OutputA,
            Valid => '1',
            OutValid => open
         );
end architecture;

The code references the VHDL library MercurySupport, this is a Liquid Instruments library and further information on its contents is available on the Help section of the MCC website. Specifically the entity ScaleOffset is named. This entity is an FPGA specific hardware block that is dedicated to multiply and add functions. This entity is instantiated as block ‘DSP’ and used to provide math function of :

Output = (Input*Scale) + Offset

Both scale and offset are 16-bit, signed 2’s complement numbers. Scale is mapped from -1 to +1.  Additionally the output, Z, is clipped to prevent over or under flowing of the math operation.

Another new feature of this example is the use of Control1 and Control2. These control registers are accessible from the Moku web browser interface and thus provide a way to provide input parameters to the MCC instrument.

VHDL example #4a: output limit setting

Example #4 provides a way to clip an output signal to an upper (or lower) limit.

library IEEE;
use IEEE.Numeric_Std.all;
use WORK.MercurySupport.clip;

architecture Behavioural of Customwrapper is
begin
    OutputA <= resize(clip(InputA, 8, 0), 16);
end architecture;

Just as in example #3, this example references library MercurySupport and this time calls out entity ‘clip’.

The OutputA is now assigned to the clipped, lower 9 bits of InputA. This provides 2^power clipping function.

VHDL example #4b: generic out limit setting

Example #4b provides a way to clip an output signal to an upper (or lower) limit.

library IEEE;
use IEEE.Numeric_Std.all;
architecture Behavioural of CustomWrapper is
begin
    process(Input A) is
    begin
        if InputA > 2387 then
            OutputA <= to_signed(2387, 16);
        esleif InputA < -7462 then
            OutputA <= to_signed(-7462, 16);
        else
            OutputA <= InputA;
        end if;
    end process;
end architecture;

Whereas example #4a would provide a crude power of 2 clipping,  this example provide a more generalized clipping function. The OutputA is assigned to InputA but clipped to +2387 and -7462

VHDL example #5: PWM from analog input

Example 5 is more lengthy. It generates a pulse width modulation (PWM) signal from the analog inputA. It comprises two files, Counter.vhdl and pwm.vhdl.  These are entered as separate files in MCC file editor before building together

counter.vhdl:


-- counter.vhdl

library IEEE;
use IEEE.Std_logic_1164.all;
use IEEE.Numeric_Std.all;

--Output Strobe every 2^EXPONENT / INCREMENT Input Strobes
--Will quantize to round integers but maintains overflow, so
--will average out over time, but will have a +-1 cycle jitter.
entity Counter is
	generic (
		EXPONENT : positive := 8;
		PHASE90 : boolean := false
	);
	port (
		Clk : in std_logic;
		Reset : in std_logic;
		Enable : in std_logic;
		Increment : in unsigned;
		Strobe : out std_logic
	);
end entity;

architecture Behavioural of Counter is
	signal Count : unsigned(EXPONENT downto 0);
begin

	assert Increment'length <= Count'length severity FAILURE;

	process(Clk) is
	begin
		if rising_edge(Clk) then
			if Reset = '1' then
				Count <= (others => '0');
				if PHASE90 then
					Count(EXPONENT - 1) <= '1';
				end if;
			elsif Enable = '1' then
				--Trim the MSB but allow overflow into it.  This gives a single Clk cycle
				--output pulse on Strobe.
				Count <= resize(Count(Count'left-1 downto 0), Count'length) + Increment;
			else
				Count(Count'left) <= '0';
			end if;
		end if;
	end process;

	Strobe <= Count(Count'left);

end architecture;

pwm.vhdl:


-- pwm.vhdl

library IEEE;
use IEEE.Std_Logic_1164.all;
use IEEE.Numeric_Std.all;
use WORK.MercurySupport.ScaleOffset;
use WORK.MercurySupport.clip;

architecture Behavioural of CustomWrapper is
    constant HI_LVL : signed(15 downto 0) := x"7FFF";
    constant LO_LVL : signed(15 downto 0) := x"0000";
    signal Value : signed(12 downto 0);
    signal Count : unsigned(12 downto 0);
    signal Pulse50Hz : std_logic;
    signal Pulse : std_logic;
begin
    INPUT_SCALE: ScaleOffset
        port map (
            Clk => Clk,
            Reset => Reset,
            X => InputA,
            Scale => signed(Control1(15 downto 0)), -- 1024
            Offset => signed(Control2(15 downto 0)),  -- 1024
            Z => Value,
            Valid => Pulse50Hz,
            OutValid => open
        );

    OSC: entity WORK.Counter
        generic map (24)  -- ~50Hz from 312.5MHz
        port map (Clk, Reset, '1', to_unsigned(3, 4), Pulse50Hz);

    OSC2: entity WORK.Counter
        generic map (15)  --2ms/2048 from 312.5MHz
        port map (Clk, Pulse50Hz, '1', to_unsigned(107, 8), Pulse);
      
    process(Clk) is
    begin
        if rising_edge(Clk) then
            if Pulse50Hz = '1' then
                Count <= resize(unsigned(clip(Value, 11, 0)), Count'length) + 512;
            elsif Pulse = '1' and Count /= 0 then
                Count <= Count - 1;
            end if;
        end if;
    end process;

    OutputA <= HI_LVL when Count /= 0 else LO_LVL;
end architecture;

Summary

In this application note we have explained some of the advantages and benefits of Moku Cloud Compile when operating as part of Multi Instrument Mode on Moku:Pro.  The entire process from entering the simplest VHDL case of example #1 was covered from the point of entering the HDL code, through building deploying and confirming expected operation.

Further example code was presented and briefly explained; inviting the user to experiment with the possibilities opened up by MCC.

Further CC examples of more complex math operations, custom trigger modes and other applications can be developed from these basics.


Moku:Pro Demo mode

You can download the Moku app for iPadOS for free at the Apple app store. The demo mode operates without need for any hardware and provides a great overview of using Moku:Pro and its interface.


Questions or comments?

Please contact us at [email protected]