qdosmsq:traps:trap_3:rhdr
Table of Contents
FS_HEADR/IOF_RHDR
This trap reads a file header.
| Call Parameters | Return Parameters | ||
|---|---|---|---|
| D0.B | $47 | D0.L | Error code. |
| D1.L | D1.W | Length of header read. | |
| D2.L | Buffer length | D2.L | Preserved. |
| D3.W | Timeout | D3.L | Preserved. |
| A0.L | Channel ID | A0.L | Preserved. |
| A1.L | Pointer to buffer | A1.L | Updated. |
Errors
| ERR_NC | Not complete. |
| ERR_NO | Channel not found. |
| ERR_BO | Buffer full. |
Notes
- All registers not shown above are not used on entry and are preserved on exit.
- The length of header is 64 bytes for a directory driver and 15 bytes for other device drivers.
- After the buffer has been read A1.L points to one after the last character read.
- The form of header is shown below.
- The file type (byte 5) is 0 for data files, 1 for executable files, 2 for relocatable files and 255 for subdirectories.
File Header
| Address | Length | Contents |
|---|---|---|
| $00 | long | File length |
| $04 | byte | File access set to 0 in QDOS v1.03 |
| $05 | byte | File type |
| $06 | long | Size of data space for executable files |
| $0A | long | Unused |
Additionally for Directory Drivers
| Address | Length | Contents |
|---|---|---|
| $0E | word | Length of filename |
| $10 | 36 bytes | Filename |
| $34 | long | Update date |
| $38 | word | Version number |
| $3A | word | Reserved |
| $3C | long | Backup date |
Example
The example below shows how to read the header of an executable file and put its length into D2.L.
Read_h lea -64(a7),a7 ; Space on the stack for the header.
movea.l a7,a1 ; Point to the space.
moveq #64,d2 ; Length of buffer.
moveq #-1,d3 ; Timeout.
moveq #$47,d0 ; FS_HEADR
trap #3 ; Read the header.
tst.l d0 ; OK? . .
bne error ; . . no!
movea.l a7,a1 ; Reset A1
subq.b #1,5(a1) ; Check for executable file
bne error ; OOPS!
move.l (a1),d2 ; Set file length in D2
lea 64(a7),a7 ; Tidy stack
; We could now load the file into memory.
qdosmsq/traps/trap_3/rhdr.txt · Last modified: 2009/02/17 11:47 by george.gwilt
