What's in the first 16 bytes of the compiled binary ("initialization data")?

Keith Leinenbach

What's in the first 16 bytes of the compiled binary ("initialization data")? The first 8 bytes are defined as CLKFREQ and CLKMODE, but what are the last 8?

I am curious because I wanted to know how to separate the program length from the variable length in a binary image. The Propeller Tool can differentiate these values with only a loaded binary with no code listing.

I thought it might be in the last 8 bytes, but it doesn't seem to match up.

Thanks!
Keith

Dave Hein

The first 16 bytes are defined as follows:

hub addr content
-------- -------
$0 to $3 clkfreq
$4       clkmode
$5       checksum
$6 to $7 pbase - Address of the top object. Always $10
$8 to $9 vbase - Start of VAR data.  Equal to the file size
$A to $B dbase - Start of the stack.  Equal to the program size
$C to $D pcurr - Execution start address
$E to $F dcurr - Initial value of the stack pointer

Roy Eltham

Just one minor thing to add:
vbase (start of VAR data) is only equal to the file size in *.binary files. For *.eeprom files, which are always 32k, it's not.

Roy

Keith Leinenbach

Thank you Dave. What are the last 8 bytes after the code and VAR section and is this always 8 bytes? Also, is there a handy dandy reference for information like this or did I just miss it in the docs?

Oops on CLKMODE, only 1 byte!

Keith

Dave Hein

The last 8 bytes that are shown in the HEX display of the Prop tool are the first 8 bytes that are put on the stack when a program is loaded. The value of the 8 bytes is FF FF F9 FF FF FF F9 FF, which represent a stack frame used when calling methods. The stack frame contains the return address, which is FFF9 in this case. This is used when a program aborts or returns from the first method. FFF9 is located in the ROM, and it contains a few bytecodes that stop the current cog.

These 8 bytes aren't included in a binary file, and they are added when the program is loaded to the Prop. If you add the bytes in a binary file you will get a sum of $14. If you add the 8 extra bytes to this you will get zero, so the checksum at location $0006 includes the extra bytes. The values of DCURR and DBASE normally differ by 8 due to the 8 extra bytes.

This information is not in the official Parallax documents. There is no single document with the details about how Spin operates, but you can find quite a bit of information at http://propeller.wikispaces.com/ .

Keith Leinenbach

Thanks Roy and Dave. Valuable information.

Keith