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FileSwitch
Enumerate Handles
A reason code is available within FileSwitch version 2.44 onward to enumerate file handles. This allows clients to obtain information on open files using a defined interface rather than relying on knowledge of the earlier restriction within FileSwitch of 255 file handles, allocated sequentially downward from 255.
OS_FSControl 58 (enumerate file handles)
On entry
R0 = 58 (reason code)
R1 = last handle, or -1 to start at first handle
On exit
R0 = stream status word, or preserved if no more handles exist
R1 = file handle, or -1 if no more handles exist
R2 = filing system info word, or preserved if no more handles exist
This reason code is used by clients wishing to enumerate open file handles. Clients should be aware that filing system operations may occur during the enumeration process and should take appropriate action.
Catalogue filename width
A variable, FileSwitch$NameWidth, can be set to give the width of filenames in the *Cat display. It has a minimum value of 12, and a maximum value of 255. This can be set at any time and will be read per-use of *Cat. It is present in all versions of FileSwitch since RISC OS 4.
IOCtl operations
From FileSwitch 2.36 onward support has been added for IOCtl calls. These allow 'control' commands from the client opening the file. An OS_Args reason code has been added to support this, and a new bit added to the extra filing system information word.
OS_Args 9 (IOCtl)
On entry
R0 = 9 (reason code)
R1 = file handle
R2 = pointer to parameter block
On exit
R0-R2 preserved
This call is used by clients wishing to control devices at the other end of a file handle. This may be used for filing specific operations. This operation will be passed to the FileSystem Args entry as reason code 11.
The IOCtl parameter block takes the following form :
+0 - Flags:
bits 0-15 = IOCtl reason code
bits 16-23 = IOCtl group code :
0 = Serial group operations
1 = Parallel group operations
255= Generic group operations
bits 24-29 = reserved (must be 0)
bit 30 = set to read data
bit 31 = set to write data
+4... Data for operation
Parallel IOCtl operations
The following parallel IOCtl operation reason codes are supported by the parallel device driver :
- Read Device ID size
- Read Device ID data
- Read Reverse Nibble status size
- Read Reverse Nibble status data
In each case the first word of the data indicates the size of the buffer.
Serial IOCtl operations
The following serial IOCtl operation reason codes are defined for serial devices :
1 Baud rate
One word containing the baud rate (bits per second)
2 Data format
One word containing flags indicating data format:
bit 0-7 = data length (5,6,7 or 8)
bit 8-15 = number of stop bits (1 or 2)
bit 16-23 = parity encoded as
0 = no parity
1 = even parity
2 = odd parity
others reserved
bit 24-31 = reserved
3 Handshake
One word containing the handshaking type:
0 = no handshaking
1 = RTS/CTS handshaking
2 = XON/XOFF handshaking
3 = DTR/DSR handshaking
others reserved
4 Buffer size
Size of buffer used for transfers
5 Buffer Threshold
Trigger for handshaking or upcall notification
6 Control lines
One word containing flags :
bits 0-15 read/write:
bit 0 : DTR
bit 1 : RTS
bit 2-15 : reserved
bits 16-31 read only:
bit 16 : CTS
bit 17 : DSR
bit 18 : RI
bit 19 : DCD
bit 20 : FIFOs enabled
bit 21-31 : reserved
7 FIFO trigger
Number of bytes in FIFO before an interrupt is generated.
8 Read number of baud rates
Returns a word containing the number of baud rates available
9 Read baud rate index
Supplies one word of index numbers and reads the baud rate associated
with that index.
10 Flush buffer
Flushes buffer on write; undefined on read
11 Read IR capabilities
One word containing flags :
bit 0 = IrDA capable
bit 1 = Consumer IR capable
bit 2 = ASK-IR capable
bit 3-31 = reserved
12 IR status
One word containing the type of IR:
0 : Wired
1 : IrDA
2 : ConsumerIR
3 : Ask-IR
Others reserved
Generic IOCtl operations
The following IOCtl operations have been defined for generic operations :
- Non-blocking operation. A word containing 0 for blocking operation, any other value indicating non-blocking operation
- Buffer threshold. A word indicating a point in the buffer at which a notification will be raised.
- Flush stream. No data; writing causes all pending data to be discarded
- Timeout. Time in centiseconds before a blocking operation should be considered failed.
Filing system redeclaration
As a reminder, PRM 2-524 indicates that filing systems should redeclare themselves to FileSwitch when Service_FSRedeclare is issued. Some external filing systems do not do this and thus cannot cope when the FileSwitch module is restarted.
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