We recently replaced our original "Small C" interpreter running in the SRV-1 firmware with a very powerful C interpreter called picoC - http://code.google.com/p/picoc/ - which supports a substantial subset of the full C language syntax.  
 
A few tips on using the C interpreter:
 
-  Make certain you are running the latest version of srv1.ldr firmware from  
    http://code.google.com/p/surveyor-srv1-firmware/source/checkout    or
    http://code.google.com/p/surveyor-srv1-firmware/downloads/list
 
-  A preliminary description of picoC commands is found at  
    http://www.surveyor.com/C.html  
 
-  picoC supports a "stored program" mode and an "interactive" mode.  'Q' launches the stored program mode.  '!' launches the interactive mode.  Note that when a stored program finishes running, picoC switches to interactive mode which allows you to continue accessing variables and functions that were defined by the stored program.
 
-  The stored program mode runs programs from the flash buffer located in SDRAM (addr 0x00100000).  This is the same flash buffer that's used for srv1.ldr firmware uploads.  It is possible to directly enter code into the flash buffer using the 'E' editor, but a more secure method is to use XMODEM file transfer (the same method that is used to transfer srv1.ldr firmware updates.  
 
-  After initiating an XMODEM session via the 'X' command, you need to transfer your C source code via XMODEM-CRC or XMODEM-1K protocol.  On Windows, the TeraTerm terminal program - http://www.ayera.com/teraterm/ - has very good support for XMODEM transfers.  On OS/X or Linux, we use the lrzsz transfer program - http://www.ohse.de/uwe/software/lrzsz.html .  With the rest of the SRV-1 source code, you'll find shell scripts to automate this transfer - take a look at 'send1' (for arbitrary file transfer) and 'load1' (for srv1.ldr transfer).
 
-  After the C source has been uploaded to the flash buffer, you can verify that it has been transferred by sending the 'zd' command to dump the contents of the flash buffer.  You can also save you C source to flash memory - the 'zw' command saves the flash buffer contents to flash sector #4, and the 'zr' command retrieves the flash sector #4 contents to the flash buffer.  
 
-  You aren't limited to storage/retrieval from flash sector #4.  There are 64 x 64kB flash sectors numbered 00 - 63, and the 'zW' and 'zR' commands allow you to save/retrieve the flash buffer contents to any flash sector except sectors 0 and 1 where srv1.ldr is stored.    
 
- Everything happens through the "flash buffer" - we use the same buffer for uploading new firmware, saving and retrieving data from flash memory, uploading and running C interpreter programs.
 
Here is a summary of commands for manipulating the flash buffer -  
 
X  -  for XMODEM receive
zc -  clear the flash buffer
zd  - display the contents of the flash buffer
zr -  retrieve the contents of flash sector 04
zw - write the flash buffer to flash sector 04
zR - retrieve the contents of any arbitrary flash sector 02-63
zW - write the contents of the flash buffer to any arbitrary flash sector 02-63
zC - compute the CRC-16 of flash buffer contents
E  - simple line editor which writes directly into the flash buffer
Q  - launches C interpreter to run contents of flash buffer
 
As noted above, if you use XMODEM to transfer a file, you can view the contents of the buffer using 'zd'.  If you want to save the contents, use 'zw' or 'zWxx'.  
 
-  It is somewhat easier to use the C interpreter in interactive mode with a line-based terminal such as telnet in "line mode" or nc ("netcat"), as the interpreter doesn't have an erase or backup key.  A Windows version of nc is found here -  
    http://www.surveyor.com/blackfin/nc111nt.zip
 
-  There is no "main()" function in picoC.  Take a look at the code samples in http://www.surveyor.com/C.html - any of those should be able to run as complete standalone programs, e.g.
Code:

int x, y, z;
for (x = 0; x < 2; x++)
{
  for (y = 0; y < 3; y++)
  {
    for (z = 0; z < 3; z++)
    {
	printf("%d %d %d\n", x, y, z);
    }
  }
} 

 
Questions about using the new C interpreter should be posted here.  Also, we would like to see interesting code samples posted here.  At some point, I hope we can build a repository of such samples.

After running a stored program, is there any way from the interactive mode to rerun the program, so that data is preserved from one run to the next?  I would guess that dropping out of interactive mode with <ESC> and then restarting the program with "Q" from the main Surveyor loop would reset all data.

Quote from admin on 04/14/09 at 2:57pm:

That should work fine.  Thanks.

Correct - you need to ignore the old c.c.  Take a look at Makefile - it builds from the picoc subdirectory.  We need to clean out some of the old files in the code repository.

Yes - we got rid of "silent console".  I don't recall the change from int to unsigned int, but it might have resulted from an effort to get rid of all compiler warnings after adding -Wall to the gcc command.
 
I just cleaned out a bunch of the old files from the svn repository.
 
One unfinished piece of business is to add direct access from picoC to the neural net data structures.  In particular, it would be nice to be able to reconfigure the neural net on-the-fly so that we're not limited to the current fixed structure of 64 inputs, 16 hidden, and 16 outputs.  I haven't decided how to approach this, but it's moving toward the top of the TODO list.
 

You can access globals to read - in fact, you can see how access to globals is defined at the top of library_surveyor.c, though we defined the globals as read only.  I have not tried write access.  
 
By the way, I did connect the picoc neural functions so that the output neurons can be accessed.  This will be in the next code update.

I don't have the code in front of me at the moment,  but there is a wiki on the picoc google site that covers these extensions.  Look at library_surveyor.c for examples of linking to firmware functions.

Where are xoff, x1 and x2 declared ?  Do you have "extern" statements somewhere so that they can be referenced between different code modules ?