Free Routine Entry (changes)
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Filer_Action
» SWI Calls
» Free Routine Entry
Free Routine Entry
Routines available
| R0 | Use |
|---|---|
| 0 | No Op – |
| 1 | Get device name – you should place the device name at R2 and the length of the name in |
| 2 | Get free space for device – used to find the free space on a device, which should be written to the buffer. Reason code 4 is is now the |
| 3 | Compare device – used to check if a file exists on a particular drive. A fast filing system such as RAMFS is allowed to always return Z |
| 4 | Get free space for device (64 bit) – 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 |
Reason code 0 – No Op
| Entry | ||
|---|---|---|
| R0 | R0 | 0 (reason code) |
| Exit | |
|---|---|
| All Register Preserved |
Reason code 1 – Get device name
| Entry | |
|---|---|
| R0 | 1 (reason code) |
| R1 | Filing System Numbers |
| R2 | Pointer to buffer |
| R3 | Pointer to device or ID |
| Exit | |
|---|---|
| R0 | Length of |
| R1 | Preserved |
| R2 | Preserved |
| R3 | Preserved |
Reason code 2 – Get free space for device
| Entry | |
|---|---|
| R0 | 2 (reason code) |
| R1 | Filing System Numbers |
| R2 | Pointer to 3 word buffer (See below) |
| R3 | Pointer to device or ID |
| 3 word buffer | |
|---|---|
| Offset | Meaning |
| +0 | Total size of device (0 if unchanged) |
| +4 | Free space on device |
| +8 | Used space on device |
| Exit | |
|---|---|
| R0 | Preserved |
| R1 | Preserved |
| R2 | Buffer provided upon entry is updated |
| R3 | Preserved |
Reason code 3 – Compare Device
| Entry | |
|---|---|
| R0 | 3 (reason code) |
| R1 | Filing System Numbers |
| R2 | Pointer to filename |
| R3 | Pointer to device or ID |
| R6 | Pointer to special field |
| Exit | |
|---|---|
| R0 | Preserved |
| R1 | Preserved |
| R2 | Preserved |
| R3 | Preserved |
| R6 | Preserved |
Z flag is set if R2, R6 point to a file on R3.
Reason code 4 – Get free space (64 bit)
| Entry | |
|---|---|
| R0 | 4 (reason code) |
| R1 | Filing System Numbers |
| R2 | Pointer to 6 word buffer |
| R3 | Pointer to device name or ID |
| 6 word buffer | |
|---|---|
| Offset | Meaning |
| 0, 4 | Total size of device (0 if unchanged) |
| 8, 12 | Free space on device |
| 16, 20 | Used space on device |
Note:
- Word 0 is bits 0 – 31
- Word 1 is bits
bits32 – 63
| Exit | |
|---|---|
| R0 | 0 |
| R1 | Preserved |
| R2 | Buffer provided upon entry is updated |
| R3 | Preserved |
| R6 | Preserved |
Use
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:
Notes
- 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 (OS_FSControl 49 for reason 2, but this still alters registers that must be preserved somewhere…).
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 (OS_FSControl 49 for reason 2, but this still alters registers that must be preserved somewhere…)
The routine should exit using:
LDMIA R13!,{PC}
Notes
Don’t return an error for unused reason codes, instead return with registers preserved, to allow for future extensions to be handled in the same manner as reason code 4 was added.
See also
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