What's in the 'Initialization' section?

RossH · 2008-07-21 06:46

The first $10 bytes of Propeller code are labelled 'Initialization' when you look at them in the Propeller IDE. I know a couple of longs are used for the CLK and FREQ values, but what are the others used for? All I can find in the manual are that these are the "initial interpreter pointers"

I have written a high resolution VGA driver which uses whatever free RAM is available to implement a virtual screen bitmap. But currently I have to manually tell the program where the free RAM starts. I am sure that one of the values in the Initialization section has this value - there are a couple of values in there that look to be likely candidates, but I'm not sure which one to use.

Does anyone have a definition for what these other Initialization values are?

Thanks,

Ross.

RossH · 2008-07-21 06:56

After a few more searches I think I found what I needed in this thread:

http://forums.parallax.com/forums/default.aspx?f=25&m=221434

But it still be good to get some "official" confirmation from Parallax.

Ross.

Mike Green · 2008-07-21 12:50

Here's the information:

$0000: XX XX XX XX - internal clock frequency in Hz (long)
$0004: XX                - value to be written to clock register (byte)
$0005: XX                - checksum so that all RAM bytes will sum to 0 (modulus 256)
$0006: XX XX           - 'pbase' (word) must be $0010
$0008: XX XX           - 'vbase' (word) number of longs loaded times 4
$000A: XX XX           - 'dbase' (word) where two $FFF9FFFF's get placed
$000C: XX XX           - 'pcurr' (word) points to Spin code
$000E: XX XX           - 'dcurr' (word) points to local stack (above $FFF9FFFF)

hippy · 2008-07-21 13:04

And in graphical form ...

                           .----------.
                           |__________|         Long : Frequency (Hz)
                           |__|                 Byte : XTAL mode
                           |__|__               Byte : Checksum
                .----------|_____|              Word : Base of program
            .---|----------|_____|              Word : Base of variables
          .-|---|----------|_____|              Word : Base of stack
          | | .-|----------|_____|              Word : Initial program counter
        .-|-|-|-|----------|     |              Word : Initial stack pointer
        | | | | |          `-----'
        | | | | |
        | | | | |          .----------.
        | | | | `-> .------|__________|    +0   Pointer to next object
        | | | |     |   .--|__________|    +1   Pointer to first method
        | | | |     |   |  |__________|
        | | | |     | .-|--|          |    +N   Pointer to last method
        | | | |     | | |  |----------|
        | | | |     | | |  | DAT      |         Data Area
        | | | |     | | |  |----------|
        | | | `---> | | `->| PUB      |
        | | |       | |    :          :         Methods
        | | |       | `--->| PRI      |
        | | |       |      `----------'
        | | |       |      .----------.
        | | `-----> `----->| vars     |        Main Program Variables
        | |                |          |
        | |                `----------'
        | |                .----------.
        | `--------------->| stack    |         Stack Space
        `----------------->|          |
                           `----------'

There's no easy way to tell where the last byte of used Ram is as that depends upon the stack space used at run-time. It is possible to know the start of stack ( through word[noparse][[/noparse]$000A] ) which would give an indication of how much free Ram there were when the program starts.

You could run your program using minimal Ram then check where the stack 'high-water mark' was to get a ballpark idea of stack space being used once you'd exercised the code.

RossH · 2008-07-22 01:43

Thanks Mike and hippy.

What's in the 'Initialization' section?

Comments