On the Commodore C128 it was possible to auto-boot a floppy disk that's in the drive when the system is powered up. This does NOT work on the C64.
This only works if Track 1 Sector 0 is allocated and contains a specific signature.
I don't have a C128 so I cannot confirm this, only know of this functionality as it's mentioned in some documentation
about the disk format and even then they are not 100% certain if even this is accurate.
Boot sector format
| Byte | Content | Description | |||||
|---|---|---|---|---|---|---|---|
| 00 | Signature | Auto-boot Signature "CBM" | |||||
| 01 | |||||||
| 02 | |||||||
| 03 | Additional sectors | Track/Sector address or 0x0000 for none | |||||
| 04 | |||||||
| 05 | Bank | Bank for additional sectors, default 0x00 | |||||
| 06 | Load count | Number of sectors to load, default 0x00 | |||||
| 07 | Boot message | 0x00 terminated string, can be just 0x00 for "BOOTING..." | |||||
| 08+b | Program name | 0x00 terminated string, can be just 0x00 for none | |||||
| 09+b+p | Boot Loader | Boot Loader code, padded with 0x00 | |||||
| FF | |||||||
Example 1
This is from lemon64.com which has an example of a boot sector in DASM.
In this instance it autoboot's CPM:
Boot loader:
C128 boot sector. (T1, S0)
Compile without a load address. {-f3}
processor 6502
org0x0b00
byte"CBM"Auto boot signature
word0x0000Load address for additional sectors. (T1, S1)
byte0x00Bank number for additional sectors.
byte0x00Number of sectors to load.
byte"", 0x00Boot message: "BOOTING..."
byte"", 0x00Program to load on boot.
startldx#<cmd-1Address of command -1
ldy#>cmd
jmp0xafa5Execute BASIC command
cmdbyte"OPEN1,8,15,", $22
byte"CD:CPM.D64", $22
byte":CLOSE1:BOOT"
org0xbff, 0x00Fill with 0x00 to make 256 bytes
byte0x00
Example 2
This is from C128BOOT.txt which seems to be different to the above.
| 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 0A | 0B | 0C | 0D | 0E | 0F | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 00 | 43 | 42 | 4D | 00 | 0C | 00 | 02 | 00 | 00 | A5 | D7 | C9 | 80 | F0 | 03 | 20 | Code |
| 10 | 5F | FF | A9 | 05 | 8D | 06 | D5 | A9 | 4E | 8D | 00 | FF | 4C | 00 | 0C | ||
| 20 | All 0x00 | Blank | |||||||||||||||
| F0 | |||||||||||||||||
The code for the above loader is:
Boot loader:
ORG0x0c00start at 0x0c00 as defined in bytes 3 & 4 of boot sector
bootloaderLDA0xD7If 0xD7 = 0x80 then do some initialisation
CMP#0x80
BEQinit
JSR0xFF5FCall unknown OS call but why JSR not JMP?
initLDA#0x05Initialise 0xD506 to 5
STA0xD506
LDA#0x4Eand 0xFF00 to 0x4e
STA0xFF00
JMPbootloaderRestart the boot loader