qdosmsq:traps:trap_3:shdr
Table of Contents
FS_HEADS/IOF_SHDR
This trap sets a file header.
| Call Parameters | Return Parameters | ||
|---|---|---|---|
| D0.B | $46 | D0.L | Error return. |
| D1.L | D1.W | Length of header set. | |
| D3.W | Timeout | D3.L | Preserved. |
| A0.L | Channel ID | A0.L | Preserved. |
| A1.L | Base of header definition | A1.L | End of header definition. |
Errors
| ERR_NC | Not complete. |
| ERR_NO | Channel not open. |
Notes
- All registers not shown above are not used on entry and are preserved on exit.
- This trap sets the first 14 bytes of the file header.
- Note that if this trap is dealing with a purely serial device the length of header in D1.W will be a spurious 15.
- The format of a header is given here.
Example
The example below shows the use of this trap call to increase the dataspace of a program by $1000 bytes. It is assumed that A0 contains the file's ID and that a 64-byte buffer is at buf(A6).
datsp moveq #fs_headr,d0 ; $47
moveq #64,d2 ; Space for 64-byte header
moveq #-1,d3 ; Timeout
lea buf(a6),a1 ; Buffer
trap #3 ; Read header
tst.l d0 ; OK . .
bne error ; . . no!
add.l #$1000,buf+6(a6) ; Add $1000 to the dataspace
moveq #fs_heads,d0 ; $46
lea buf(a6),a1 ; Reset the header base address
trap #3 ; Write header
tst.l d0 ; OK . .
bne error ; . . no!
qdosmsq/traps/trap_3/shdr.txt · Last modified: 2009/05/27 15:41 by george.gwilt
