View source for GeneveOS Device Operation

Accessing devices (floppy disk, hard disk, serial connector, printer) is possible in GeneveOS via XOP calls.

== User-task XOPs ==

User-task XOPs are available for use in application programs. Here is a typical example:

 PABADD EQU  >F180   
 FILE   DATA 8
 ...
        LI   R0,PABADD
        XOP  @FILE,0
        MOVB @PABADD+2,R0
        JNE  ERROR
        ...

Similar as with the TI-99/4A device service routine concept (DSR), a Peripheral Access Block (PAB) must be set up prior to invoking the XOP.

=== Device Service Routine Call ===

{| class="xoparg"
|-
|
! Input !! Output
|-
| R0
| Pointer to PAB || -
|-
|}

The actual operation is contained in the Peripheral Access Block (PAB).

=== Peripheral Access Block ===

While the TI-99/4A DSRs expect the PAB to be stored in VDP RAM, the Geneve OS DSRs use CPU RAM for the PAB, which means the PAB need not be copied to the video RAM before use. Also, you can choose to have the I/O buffers in VDP or CPU RAM.

The general layout of the PAB is as follows:

{| class="plainc" style="margin-left:1%"
|-
! width="5%" | 00 
! width="5%" | 01 
! width="5%" | 02 
! width="5%" | 03 
! width="5%" | 04 
! width="5%" | 05 
! width="5%" | 06 
! width="5%" | 07 
! width="5%" | 08 
! width="5%" | 09 
! width="5%" | 0A 
! width="5%" | 0B 
! width="5%" | 0C 
! width="5%" | 0D 
! width="5%" | 0E 
! width="5%" | 0F 
! width="5%" | 10 ...
|-
| Opcode 
| Mode
| Error code
| colspan="3" | Buffer address
| colspan="2" | Record number
| colspan="2" | Record length
| Memory type
| colspan="3" | Character count
| Status byte
| Name length
| Name
|-
|}

Note that the buffer addresses are 21-bit wide, represented by the [[MDOS Memory Management Functions#Local_.28virtual.29_pages | virtual address]] within the calling task. The address for this buffer should be derived from [[MDOS Memory Management Functions | memory allocation]] operations that were invoked earlier. 

After the operation, the PAB contains information about the results of the operation.

=== Mode ===

The mode bits are used to determine the operation direction (in/out/update/append), the encoding (display/internal), the structure (fixed/variable) and the access (sequential/relative).

{| class="plainbits" style="width:64%"
! 0
! 1
! 2
! 3
! 4
! 5
! 6
! 7
|-
| style="width:24%" rowspan="4" colspan="3" | Unused (000)
| style="width:8%" rowspan="2" | Fixed=0
| style="width:8%" rowspan="2" | Display=0
| style="width:16%" colspan="2" | Update=00
| style="width:8%" rowspan="2" | Sequential=0
|-
| colspan="2" | Output=01
|-
| rowspan="2" | Variable=1 
| rowspan="2" | Internal=1
| colspan="2" | Input=10
| rowspan="2" | Relative=1
|-
| colspan="2" | Append=11
|}


=== Error code ===

The error code is an eight bit word with the following structure:

{| class="plainbits" style="float:left"
! 0
! 1
! 2
! 3
! 4
! 5
! 6
! 7
|-
| colspan="3" | Number
| colspan="5" | Detail code for error 7
|}

{| class="plainc" style="float:left"
! Number
! Meaning
|-
| 0
| No such device
|-
| 1
| Write-protected
|-
| 2
| Illegal open attribute
|-
| 3
| Illegal operation
|-
| 4
| Out of buffer space
|-
| 5
| Read beyond EOF
|-
| 6
| Device error
|-
| 7
| File error
|}

<div style="clear:both"></div>

== Operations ==

=== OPEN ===

Open a record-oriented file. A file must be opened before it can be read from or written to. This operation is not required for flat memory image files.

The PAB must be set up prior to invoking the operation:

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''00'''
| Mode
| -
| colspan="3" | -
| colspan="2" | Records to reserve
| colspan="2" | Record length
| -
| colspan="3" | -
| -
| Name length
| Name
|-
|}

'''Open new file''': The '''Record Length''' must be set to a value greater than 0. This will become the length of the records of the new file.

'''Open existing file''': The '''Record Length''' must match the length of the records. If the length is unknown, 0 may be passed.

After the OPEN operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | -
| colspan="2" | -
| colspan="2" | Actual Record Length
| -
| 0
| colspan="2" | True Record Length
| -
| Name length
| Name
|-
|}

The '''Actual Record Length''' is the length of the records of the existing file. When 0 was passed on the call, this delivers the record length of the file; otherwise this is the value that was passed for the call. The '''True Record Length''' is the record length of the file when it already exists.

<div style="margin-bottom:6em"></div>

=== CLOSE ===

Closes a record-oriented file. A file must be closed after being used. After closing, no further read or write operations may be invoked on the file. This operation is not required for flat memory image files.

The PAB must be set up prior to invoking the operation:

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''01'''
| Mode
| -
| colspan="3" | -
| colspan="2" | -
| colspan="2" | -
| -
| colspan="3" | -
| -
| Name length
| Name
|-
|}

After the CLOSE operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | -
| colspan="2" | -
| colspan="2" | -
| -
| colspan="3" | -
| -
| Name length
| Name
|-
|}

<div style="margin-bottom:6em"></div>

=== READ ===

Reads a record from a record-oriented file. For flat memory image files, [[#LOAD | LOAD]] must be used. 

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''02'''
| Mode
| -
| colspan="3" | Buffer address
| colspan="2" | Record number
| colspan="2" | Record length
| Memory
| colspan="3" | -
| -
| Name length
| Name
|-
|}

Use the '''Record number''' field to specify the desired record in '''fixed record length''' files. This is not available for variable length record files.

The '''Record Length''' must match the length of the records as specified by [[#OPEN | OPEN]].

The '''Memory''' flag determines whether the data are read into CPU (0) or VDP (not 0) memory.

After the READ operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | -
| colspan="2" | Next record number
| colspan="2" | -
| -
| colspan="3" | Number of read bytes
| -
| Name length
| Name
|}

'''Next record number''' applies for fixed record length files only.

<div style="margin-bottom:6em"></div>

=== WRITE ===

Writes a record to a record-oriented file. For flat memory image files, [[#SAVE | SAVE]] must be used. 

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''03'''
| Mode
| -
| colspan="3" | Buffer address
| colspan="2" | Record number
| colspan="2" | Record length
| Memory
| colspan="3" | Number of bytes to write
| -
| Name length
| Name
|-
|}

Use the '''Record number''' field to specify the desired record in '''fixed record length''' files. This is not available for variable length record files.

The '''Record Length''' must match the length of the records as specified by [[#OPEN | OPEN]].

The '''Memory''' flag determines whether the data written from CPU (0) or VDP (not 0) memory.

After the WRITE operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | -
| colspan="2" | Next record number
| colspan="2" | -
| -
| colspan="3" | Number of read bytes
| -
| Name length
| Name
|}

'''Next record number''' applies for fixed record length files only.

<div style="margin-bottom:6em"></div>

=== RESTORE ===

<div style="margin-bottom:6em"></div>

=== LOAD ===

<div style="margin-bottom:6em"></div>

=== SAVE ===

<div style="margin-bottom:6em"></div>

=== DELETE ===

<div style="margin-bottom:6em"></div>

=== SCRATCH ===

<div style="margin-bottom:6em"></div>

=== STATUS ===

<div style="margin-bottom:6em"></div>

=== BREAD ===

Reads a sector from a file or from a device. This is a level-2 operation, that is, it accesses the device based on sector addressing (or sectors of a file). BREAD allows for two operations:

* Read sectors from a file.
* Read sectors from a device.

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''0A'''
| -
| -
| colspan="3" | Buffer address
| colspan="2" | Sector offset LSW
| colspan="2" | -
| CPU / VDP
| -
| colspan="2" | Number of sectors
| Sector offset MSB
| Name length
| Name
|-
|}

The sector offset is defined by byte 0E as the most significant byte (value*65536) plus the word in bytes 06 and 07.

Byte 0A specifies whether the buffer address belongs to the CPU (0) or the VDP (non-zero) address space.

'''Read from file''': When a file is addressed, the operation reads a sequence of sectors from the file. The '''Sector offset''' is the number of the first sector of the file, counting from 0. The physical locations of the sectors are subject to the sector allocation on the device.

'''Read from device''': When a device is addressed, the operation reads a sequence of sectors from the device. The '''Sector offset''' is the physical sector number.

After the BREAD operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | Updated buffer address
| colspan="2" | Updated sector offset LSW
| colspan="2" | -
| -
| -
| colspan="2" | Remaining sectors
| Updated sector offset MSB
| -
| -
|-
|}

'''Error codes'''

* '''60''': Bad operation; happens when the device is not a block device.
* '''A0''': Read beyond end of file or device. 
* '''C0''': Media error. The system was unable to read the sector although it should be readable.
* '''E0''': General error; happens when the device does not contain the specified file.

The '''Updated buffer address''' points to the memory address after the sectors were read (e.g. when 4 sectors are read, the pointer is increased by 4*256 = 1024).

The '''Updated sector offset''' is the first sector that has not been read due to an error condition.

The '''Remaining sectors''' is the number of unread sectors due to an error condition.

=== BWRITE ===

Writes a sector to a file or to a device. This is a level-2 operation, that is, it accesses the device based on sector addressing (or sectors of a file). BWRITE allows for three operations:

* Create a new, empty file.
* Write sectors to a file.
* Write sectors to a device.

'''IN'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| '''0B'''
| -
| -
| colspan="3" | Buffer address
| colspan="2" | Sector offset
| colspan="2" | -
| -
| colspan="3" | Number of sectors
| -
| Name length
| Name
|-
|}

'''Create a file''': When a file is addressed, and the number of sectors is 0, a new file is created. The contents of the file should be written by BWRITE on the same file with a sector count greater than 0.

'''Write to file''': When a file is addressed, the operation writes a sequence of sectors to the file. The '''Sector offset''' is the number of the first sector of the file, counting from 0. The physical locations of the sectors are subject to the sector allocation on the device; in particular, when fragmentation is required, the sectors are written to the new fragment.

'''Writing to device''': When a device is addressed, the operation writes a sequence of sectors to the device. The '''Sector offset''' is the physical sector number.

After the BWRITE operation has completed, the PAB delivers information about the result:

'''OUT'''

{| class="plainc" style="margin-left:1%"
|-
! width="4%" | 00 
! width="4%" | 01 
! width="4%" | 02 
! width="4%" | 03 
! width="4%" | 04 
! width="4%" | 05 
! width="4%" | 06 
! width="4%" | 07 
! width="4%" | 08 
! width="4%" | 09 
! width="4%" | 0A 
! width="4%" | 0B 
! width="4%" | 0C 
! width="4%" | 0D 
! width="4%" | 0E 
! width="4%" | 0F 
! width="4%" | 10 ...
|-
| -
| -
| Error code
| colspan="3" | Updated buffer address
| colspan="2" | Next unwritten sector
| colspan="2" | -
| -
| 0
| colspan="2" | Number of unwritten sectors
| -
| Name length
| Name
|-
|}

The '''Updated buffer address''' points to the memory address after the sectors were written (e.g. when 4 sectors are written, the pointer is increased by 4*256 = 1024).

The '''Next unwritten sector''' is the first sector that has not been written due to an error condition.

The '''Number of unwritten sectors''' is the number of unwritten sectors due to an error condition.

<div class="warn">Unless you want to write directly to the device, make sure that the PAB contains a file name that points to a file, not to a device. For example, when the file name has been created by the program, and for some reason the file name is empty (like "HDS1."), the following write operation will overwrite the volume information block and the allocation tables and '''destroy the target device filesystem'''.</div>

Tick here: [ ] Yes, I fully understood the danger of this operation.

(The author lost a complete hard disk by this incident, and was lucky to have a backup.)

<div style="margin-bottom:6em"></div>

=== PROTECT ===

<div style="margin-bottom:6em"></div>

=== RENAME ===

<div style="margin-bottom:6em"></div>

=== FORMAT ===