Apple II SP over SLIP - FujiNetWIFI/fujinet-firmware GitHub Wiki
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:
- SLIP frames allow to detect packet boundaries without parsing the (variable sized) packets.
- 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.
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.
Status Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($00) |
| 1 | SmartPort Unit Number |
| 1 | Status Code |
Status Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
| [n] | Status List (if Status == $00) |
ReadBlock Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($01) |
| 1 | SmartPort Unit Number |
| 2 | Block Size* |
| 3 | Block Number |
ReadBlock Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
| [N] | Block Data (if Status == $00) |
WriteBlock Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($02) |
| 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
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($03) |
| 1 | SmartPort Unit Number |
Format Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
Control Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($04) |
| 1 | SmartPort Unit Number |
| n | Control List |
Control Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
Init Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($05) |
| 1 | SmartPort Unit Number |
Init Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
Open Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($06) |
| 1 | SmartPort Unit Number |
Open Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
Close Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($07) |
| 1 | SmartPort Unit Number |
Close Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
Read Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($08) |
| 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) |
Write Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($09) |
| 1 | SmartPort Unit Number |
| 2 | Byte Count |
| 3 | Address |
| n | Write Data |
Write Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |
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.
Reset Request
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Command Number ($0A) |
| 1 | SmartPort Unit Number |
Reset Response
| Size | Content |
|---|---|
| 1 | Request Sequence Number |
| 1 | Status |