Apple II SP over SLIP

SmartPort over Serial Line Internet Protocol (SP-over-SLIP) is related to Apple II Protocol Converter Bus (CBus). From a high-level perspective it transports almost the same data as CBus, but the actual coding of the data is pretty different. The primary difference in the transported data results from the fact that SP-over-SLIP runs on a point-to-point connection while CBus runs - nomen est omen - on a bus.

SP-over-SLIP can be used on any medium providing a transparent, duplex, lossless byte stream. Examples are a TCP connection or a USB CDC-ACM connection.

SP-over-SLIP strictly consists of request/response packets. Every packet is encapsulated in a SLIP frame for two reasons:

1. SLIP frames allow to detect packet boundaries without parsing the (variable sized) packets.
2. SLIP frames allow to detect incomplete packets caused by an Apple II Reset during packet transmission.

Every request/response packet starts with a Request Sequence Number for this reason: An Apple II Reset after sending a request but before receiving the response makes the response stay in some TCP or USB related buffer. Now the next send request / receive response sequence receives that wrong, old response. The Request Sequence Number allows to detect (and discard) that response.

A SLIP message consists of a message enclosed by $C0

• if the contents of the message contains a $C0, transmit $DB $DC instead
• if the contents of the message contains a $DB, transmit $DB $DD instead

Example dummy message:

message:         01 DB    49 C0    15
message sent: C0 01 DB DD 49 DB DC 15 C0

Status Request (0x00)

The Status call returns information about a particular device or about the SmartPort itself. Only Status calls that return general information are listed here.

Size	Content
1	Request Sequence Number
1	Command Number (0x00)
1	SmartPort Unit Number
1	Status Code

Status Code	Meaning
$00	Return device status
$01	Return device control block
$02	Return newline status (character devices only)
$03	Return Device Information Block (DIB)

Example SLIP Status Request message:

                          Sequence Number
                          |  Status Command
                          |  |  Unit Number
                          |  |  |  Status Code
                          |  |  |  |
Apple II -> FujiNet : C0 12 00 01 03 C0 

Status Response

Size	Content
1	Request Sequence Number
1	Status
[n]	Status List (if Status == $00)

General Status Byte

Bit	Meaning
7	0 = character Device, 1 = block Device
6	1 = write allowed
5	1 = read allowed
4	1 = device on line or disk in drive
3	1 = format allowed
2	1 = media write-protected (block devices only)
1	reserved; must = 0
0	1 = device currently open (character devices only

Type	Subtype	Device
$00	$00	Apple II memory expansion card
$01	$00	Apple 3.5 drive
$01	$40	UniDisk 3.5
$02		ProFile™ hard disk
$3-$9		reserved
$0A		5.25-inch disk
$B-$F		reserved

Example SLIP Status Response message:

FujiNet -> Apple II : C0 12 00 FC 18 01 00 0E 46 55 4A 49 4E 45 54 5F 44 49 53 4B 5F 30 20 20 01 40 01 0F C0
                          |  |  |  |     |  | |---16 bytes always---------------------------|  |  | |   | 
                          |  |  |  |     |  | |F  U  J  I  N  E  T  _  D  I  S  K  _ 0      |  |  | Firmware
                          |  |  |  |     |  String Length                                      |  | Version
                          |  |  |  |    /                                                      |  Subtype
                          |  |  |  Blocks on device (3 bytes)                              Device Type
                          |  |  General Status Byte
                          |  Status
                          Sequence Number

ReadBlock Request (0x01)

The ReadBlock call reads one 512-byte block from the block device specified by the unit number.

Size	Content
1	Request Sequence Number
1	Command Number (0x01)
1	SmartPort Unit Number
2	Block Size*
3	Block Number

* Note that on the Apple II implementation, all block sizes are 512 bytes, but the interface is generic, so the size must be specified in the request.

ReadBlock Response

Size	Content
1	Request Sequence Number
1	Status
[n]	Block Data (if Status == 0x00)

WriteBlock Request (0x02)

The WriteBlock call writes one 512-byte block to the block device specified by the unit number.

Size	Content
1	Request Sequence Number
1	Command Number (0x02)
1	SmartPort Unit Number
2	Block Size*
3	Block Number
n	Block Data

WriteBlock Response

Size	Content
1	Request Sequence Number
1	Status

Format Request (0x03)

The Format call formats a block device. The formatting performed by this call is not linked to any operating system; it only prepares all blocks on the medium for reading and writing. Operating-system-specific catalog information, such as bit maps and directories, are not prepared by this call.

Size	Content
1	Request Sequence Number
1	Command Number (0x03)
1	SmartPort Unit Number

Format Response

Size	Content
1	Request Sequence Number
1	Status

Control Request (0x04)

The Control call sends control information to the device. The information may be either general or device specific.

Size	Content
1	Request Sequence Number
1	Command Number (0x04)
1	SmartPort Unit Number
1	Control Code
n	Control List

FujiNet Specific Control List

Command	Byte	Content
'O'	0	open
	1-2	payload size
	3	mode read, write or both
	4	translation
	5...	url
'C'	0	close
	1-2	payload size of $00
'R'	0	read
	1-2	payload size
	3...	data
'W'	0	write
	1-2	payload size
	3...	data
'A'	0	accept
	1-2	payload size of $00
'D'	0	udp destination
	1-2	payload size
	3...	url

Control Response

Size	Content
1	Request Sequence Number
1	Status

Example SLIP Control messages:

Apple II -> FujiNet : C0 66 04 07 4F 2B 00 0C 80 4E 3A 48 54 54 50 3A 2F 2F 61 70 69 2E 6F 70 65 6E 2D 6E 6F 74 69 66 79 2E 6F 72 67 2F 69 73 73 2D 6E 6F 77 2E 6A 73 6F 6E C0 
                       .  f  .  .  O  +  .  .  .  N  :  H  T  T  P  :  /  /  a  p  i  .  o  p  e  n  -  n  o  t  i  f  y  .  o  r  g  /  i  s  s  -  n  o  w  .  j  s  o  n  . 

FujiNet -> Apple II : C0 66 00 C0 

Init Request (0x05)

The Init call causes SmartPort to execute its initialization sequence, causing a hardware reset of all devices and assigning a unit number to each device. This call is not made to a specific unit; rather, it is made to the SmartPort as a whole. This call is executed automatically on system startup or forced cold reset.

Size	Content
1	Request Sequence Number
1	Command Number (0x05)
1	SmartPort Unit Number

Init Response

Size	Content
1	Request Sequence Number
1	Status

Open Request (0x06)

The Open Request call prepares a character device for reading or writing.

Size	Content
1	Request Sequence Number
1	Command Number (0x06)
1	SmartPort Unit Number

Open Response

Size	Content
1	Request Sequence Number
1	Status

Example SLIP Open messages:

Apple II -> FujiNet : C0 65 06 07 C0 

FujiNet -> Apple II : C0 65 00 C0 

Close Request (0x07)

The Close call tells a character device that a sequence of read or write operations has ended. For a printer, this call could have the effect of flushing the print buffer.

Size	Content
1	Request Sequence Number
1	Command Number (0x07)
1	SmartPort Unit Number

Close Response

Size	Content
1	Request Sequence Number
1	Status

Example SLIP Close messages:

Apple II -> FujiNet : C0 6C 07 07 C0 

FujiNet -> AppleWin : C0 6C 00 C0 

Read Request (0x08)

The Read Request reads the number of bytes specified by the byte count parameter.

Size	Content
1	Request Sequence Number
1	Command Number (0x08)
1	SmartPort Unit Number
2	Byte Count
3	Address

Read Response

Size	Content
1	Request Sequence Number
1	Status
[n]	Read Data (if Status == $00)

Example SLIP Read messages:

Apple II -> FujiNet : C0 6B 08 07 0B 00 00 00 00 C0 

FujiNet -> Apple II : C0 6B 00 31 37 32 35 38 38 34 32 36 30 0A C0 
                       .  k  .  1  7  2  5  8  8  4  2  6  0  .  . 

Write Request (0x09)

The Write call writes the number of bytes specified by the byte count to the device specified by the unit number.

Size	Content
1	Request Sequence Number
1	Command Number (0x09)
1	SmartPort Unit Number
2	Byte Count
3	Address
n	Write Data

Write Response

Size	Content
1	Request Sequence Number
1	Status

Reset Request (0x0A)

The Apple II side of SP-over-SLIP is supposed to be implemented using some processor beside the 6502 main processor. This allows the Apple II - in contrast to CBus - to inform the connected devices about a 6502 reset. This can i.e. have a modem drop an active connection or a printer eject a partially printed page.

Size	Content
1	Request Sequence Number
1	Command Number ($0A)
1	SmartPort Unit Number

Reset Response

Size	Content
1	Request Sequence Number
1	Status