In Visual Studio:

0)  Create an empty C/C++ project.

 
In MATLAB:

1)  Write the m-file with one function to expose to C/C++.

        function [xp, length] = ExpandArray( x, interval)
        xp = 0:interval:x(length(x));
        length = length(xp);

2)  Create a deployment project (File->New->Deployment Project).

3)  Add m-file to “Exported functions” in deployment project.

4)  Change the settings of the deployment project to put the output directory output to the directory of the source files for the C/C++ project.  Set the Library Name (e.g. “Functions”).
In Visual Studio:

5)  Right-click on the project->Properties.

5a) Under C/C++->General, add the directory of the MATLAB header files to “Additional Include Directories”:

      "C:\Program Files\MATLAB\R2007a\extern\include"

5b) Under Linker->Input, add the directory of the MATLAB libraries and the location of your newly created MATLAB library to “Additional Dependencies”:

      "C:\Program Files\MATLAB\R2007a\extern\lib\win32\microsoft\mclmcrrt.lib"
      "C:\...\Functions.lib", where "..." is the path of the output directory set in step 4

6)  Add the created header file to your project and include it in your C/C++ code where appropriate.

7)  In your C/C++ code, initialize the MATLAB component:

      bool ret = FunctionsInitialize();
      if (!ret){
        std::cout << "Error initializing MATLAB Component Runtime\n";
        system("PAUSE");
        return 0;
      }

8)  Create the input variables to the MATLAB function:

      double x[4] = {1,2,3,4};
      mwArray mwX(1,4,mxDOUBLE_CLASS);
      mwX.SetData(x,4);
      mwArray mwInterval((double) 0.1);
      int nargout = 2; // this says you will be using 2 outputs, xp and length

9)  Create the output variables from the MATLAB function:

      mwArray mwXP;
      mwArray mwLength;

10) Call your function:

      ExpandArray(nargout, mwXP, mwLength, mwX, mwInterval);

11) Get the data out of the mwArrays:

      int length;
      mwLength.GetData(&length, 1);

      double *xp = new double[length];
      mwXP.GetData(xp, length);

12) Terminate the use of the MATLAB component:

      FunctionsTerminate();

 
Notes:

If you only want to return one variable from your MATLAB function, set
nargout to 1 and the return variable will be as such:
  int returnVariable = MyFunction(nargout, inputVariable);

I recently purchased a Terasic DE2-70 Cyclone II development board.  The makers have two prices:  $599 commercial and $349 academic.  If you’re a college student, the academic price is still too much.  After I got a job, made some money, and saved up, I sent the Taiwanese company Terasic a little email.  I told them I recently graduated and wanted to get the academic price, stating that I would be using it for personal learning, etc.  They were more than happy to offer the discount, so I’m now the proud owner of a DE2-70.  (By the way, they ship from Taiwan – viz. $40 shipping from the other side of the world.)

Well, having gone through Altera’s “Introduction to the Altera SOPC Builder Using VHDL Design” to remember how to use the software, I found multiple problems with the tutorial as it is.  I hope that listing the solutions here will help people in the same situation.  Some of these issues are obvious, and some are a bit more subtle.

I am using Quartus II 7.2 and  NiosII 7.2.

1. In Step 1: “In your project, choose the EP2C35F672C6 chip as the target device, because this is the FPGA on the DE2 board”. Well, the DE2-70 uses a different chip.  Choose the EP2C70F896C6.  This can be verified by simply looking at the text printed on the FPGA.
2. In Step 1: “You can choose a different directory or project name, but be aware that the SOPC Builder software does not permit the use of spaces in file names”. This is true and I just wanted to make it obvious that you can’t have a space *anywhere* in the pathname.  For example, you would have problems in SOPC  Builder if your project was in “C:\Program Files\…” since that path contains a space.
3. In Step 6: “In the On-Chip Memory Configuration Wizard window, shown in Figure 8, set the memory width to 32 bits and the total memory size to 4 Kbytes”. As I’ll be getting to shortly, the 4kB is not enough for the NiosII project.  Crank it up to 64kB for plenty of breathing room.
4. In Step 7: The PIO is under Peripherals -> Microcontroller Peripherals -> PIO (Parallel I/O).
5. In Step 9: The JTAG UART is under Interface Protocols -> Serial -> JTAG UART.
6. After Step 11: Write down the base addresses of the PIOs after auto-assigning the addresses.  These will be needed for NiosII, as they are treated as memory-mapped I/O.
7. Before Step 12: There are a couple “To Do”‘s in the message window of SOPC Builder about the NiosII CPU that need to be addressed:  the reset and exception vectors.  Double-click the NiosII component you instantiated to open up the properties window you were at before.  Now that you have on-chip memory instantiated, click on the Reset Vector and Exception Vector Memory drop-down boxes and select the name of your memory (e.g. “onchip_mem”).  Leave the offsets the way they are (0x0 and 0x20).  Don’t worry about the “Warning: Switches: PIO inputs are not hardwired in test bench. Undefined values will be read from PIO inputs during simulation.”, this tutorial doesn’t do any test benches.
8. Importing DE2_70_pin_assignments.csv.  This comma-separated file is located on the DE2-70 CD included with the kit, and it can also be found on the internets.  Mmm, google.  The naming convention for this Altera-supplied file changed from DE2 to DE2-70.  Open it and take a look.  There are now lower-case ‘i’s and ‘o’s before many of the hard-wired signals denoting them as input and output.  Remember this!  The HDL code needs to change reflecting this.  Otherwise the .csv needs changing, but I don’t suggest it.  Here’s my resulting code (remember, the port names may be different for your SOPC component):
   • LIBRARY ieee;
     USE ieee.std_logic_1164.all;
     USE ieee.std_logic_arith.all;
     USE ieee.std_logic_unsigned.all;

     ENTITY lights IS
     PORT (
     iSW        : IN    STD_LOGIC_VECTOR(7 DOWNTO 0);
     iKEY    : IN    STD_LOGIC_VECTOR(0 DOWNTO 0);
     iCLK_50 : IN    STD_LOGIC;
     oLEDG    : OUT    STD_LOGIC_VECTOR(7 DOWNTO 0)
     );
     END lights;

     ARCHITECTURE Structure OF lights IS
     COMPONENT nios_system is
     port (
     — 1) global signals:
     signal clk : IN STD_LOGIC;
     signal reset_n : IN STD_LOGIC;

     — the_LEDs
     signal out_port_from_the_LEDs : OUT STD_LOGIC_VECTOR (7 DOWNTO 0);

     — the_Switches
     signal in_port_to_the_Switches : IN STD_LOGIC_VECTOR (7 DOWNTO 0)
     );
     END COMPONENT;

     BEGIN
     NiosII:        nios_system PORT MAP(iCLK_50, iKEY(0), oLEDG, iSW);
     END Structure;

9. Before Section 3.2: If you’ve tried to do a full compilation at this point, you will probably see an unexpected error:
   • Error: Can’t place pins assigned to pin location Pin_AD25 (IOC_X95_Y2_N1)
     Info: Pin iSW[7] is assigned to pin location Pin_AD25 (IOC_X95_Y2_N1)
     Info: Pin ~LVDS195p/nCEO~ is assigned to pin location Pin_AD25 (IOC_X95_Y2_N1)
     Error: Can’t fit design in device
     Error: Quartus II Fitter was unsuccessful. 2 errors, 3 warnings
     Info: Allocated 215 megabytes of memory during processing
     Error: Processing ended: Sun Oct 18 19:11:13 2009
     Error: Elapsed time: 00:00:03
     Error: Quartus II Full Compilation was unsuccessful. 2 errors, 152 warnings
   • Here is the fix:
     • In Quartus-II select menu Assignments>Device…
     • Select button “Device and Pin Options…”
     • Select the tab “Dual-Purpose Pins”
     • Under the list of “Dual-purpose pins:” change the “Value” property of nCEO to “Use as regular I/O”.
     • Click OK
10. After Section 3.2:  If you are using the Web edition or didn’t buy the full license for the Altera IP, you probably got a pop-up window after programming the device stating “OpenCore Plus Status Click Cancel to stop using OpenCore Plus IP.  Time remaining:  unlimited”.  Do not close this window if you intend on using the NiosII IDE to run on the hardware.  Just leave the window up and close when you are done, or have a problem with Quartus or SOPC Builder.
11. I skipped over the Assembly programming section because this tutorial already gave me a headache.  I’m not a masochist.
12. In Section 4.2: When you create a new project, create it in the following way:  File -> New -> Project… and select “Nios II C/C++ Application”.  Also, use the Hello World template.  It sets everything up for you, gives you printf functionality to the console, but takes up a bit more space.
13. lights.c:  Here’s what I have in my file.  Again, it might be a bit different for the base addresses.
    • #include <stdio.h>
      #define Switches (volatile char*) 0x21000
      #define LEDs (char*) 0x21010

      int main()
      {
      printf(“Hello from Nios II!\n”);
      while (1){
      *LEDs = *Switches;
      }
      return 0;
      }

14. After all of that is done, you right-click on your project in NiosII IDE (e.g. hello_world_0) and click “Run As -> Nios II Hardware”.
15. Done!  You can now move the switches (SW7 – 0) and see the LEDG7-0 change.  You can also reset the CPU using KEY0.

I know how frustrating it can be trying to learn something when the tutorial is wrong.  Hope this helps!