0 String Pointer to string, which will be GSTransed now (will not be 0 terminated)
1 Number 4 byte integer
2 Macro Pointer to string, which will be GSTransed each time it is used
3 Expanded Expression which will be sent through OS_EvaluateExpression
4 Literal String that will not be GSTransed
+16 Code Pointer to a block of code
Variable type Code
R1 points to a block containing the following :
Offset Contents
0 This is where the OS jumps when the variable is to be written. Will normally be a branch instruction
4 This is where the OS jumps when the variable is to be read - your code may start here
When the Write entry is called :
=> R1 = value
R2 = length of value
<= R1,2,4,10-12 may be corrupted.
When the Read entry is called :
=> -
<= R0 = pointer to value
R1 may be corrupted
R2 = len of value
The two entry points are called in SVC mode, so if you call a SWI then R14 will be corrupted.
Note that OS_ReadVarVal is marked as being re-entrant, so in theory your code could be called while threaded. However, the PRM makes no mention of this, neither warning that it could happen, nor stating that the kernel makes sure that it does not happen.
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