=> R0 = 0 (NoOp)
1 (GetFSName)
2 (GetFreeSpace)
3 (CompareDevice)
4 (GetFreeSpace64)
others dependant on R0
The routine will be called in User mode with a stack consisting only of the return address (no other use should be made of it). The routine can either:
· construct a new stack.
· use the SVC stack by calling OS_EnterOS, remembering to return to User mode before returning.
· do all the hard work with a SWI (PRM suggests OS_FSControl 49 for reason 2, but this still alters registers that must be preserved somewhere...)
The routine should exit using:
· LDMIA R13!,{PC}
See also: PRM 2-512, 5a-257, 5a-665
Free GetFSName (1)
=> R0 = 1 (GetFSName)
R1 = FS number
R2 = pointer to buffer
R3 = pointer to device or ID
<= R0 = number of bytes placed into the buffer, including the terminator
R1-R3 preserved
You should expand the device or ID into a name, and copy it to the buffer at R2, and update R0.
See also: PRM 2-513, 5a-258
Free GetFreeSpace (2)
=> R0 = 2 (GetFreeSpace)
R1 = FS number
R2 = pointer to 3 word buffer
R3 = pointer to device or ID
<= R0-R3 preserved, R2 buffer :
0 = total size of device (or 0 if unchanged)
4 = free space on device
8 = used space on device
This is used to find the free space on a device, which should be written to the buffer. On RISC OS 3.60 or later, reason code 4 is used in preference to this, but this should also be supported.
See also: PRM 2-514, 5a-258
Free CompareDevice (3)
=> R0 = 3 (CompareDevice)
R1 = FS number
R2 = pointer to filename
R3 = pointer to device or ID
R6 = pointer to special field
<= R0-R3 and R6 preserved
Z set if R2, R6 point to a file on R3.
This call is used to check if a file exists on a particular drive. A fast filing system (RAMFS) is allowed to always return Z set.
See also: PRM 2-514, 5a-258
Free GetFreeSpace64 (4)
=> R0 = 4 (GetFreeSpace64)
R1 = FS number
R2 = pointer to a 6 word buffer
R3 = pointer to device name or ID
<= R0 = 0
R1 - R3 preserved, R2 buffer updated.
This is used to find the free space on a device. From RISC OS 3.60, this call is used rather than 2. If R0 is non-zero on exit, or if an error occurs, then reason code 2 is called. Thus your routine must give an error for both reason codes 4 and 2 before Free will believe it.
See also: PRM 5a-258
Buffer contents for Free GetFreeSpace64
The format of the buffer is as follows:
Offset Meaning
[0,4] total size of device (or 0 if unchanged)
[8,12] free space on device
[16,20] used space on device
The bit order for the pairs of word are:
Word Bits
0 0-31
4 32-63
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