Network protocol

Changelog

Packet structure

This protocol works on a system of requests and responses. The client will send a request to the server, with an amount of data. The server will then send a response to the client, with an amount of data.

The structure of a request and response packet, are actually identical. The only difference, is the meaning of the first byte.

The first byte, for a request, is the command number. For a response, this is the returned status for the request.

typedef struct {
    uint8_t  reqstat;       // Request number, or response status
    uint16_t datalen;       // Length of the data being sent with this request/response
    uint8_t  data[];
} packet_t;

Initial connection

Upon initial connection, the server will send 4 bytes.

The first two are a magic number, 0x64 0x73 ('DS' in hex). The third byte signifies the major version of the program, and the fourth signifies the minor version. Minor revisions will be protocol-compatible. Major revisions may not be.

CHS datatype

The CHS datatype is used often in requests/responses. It is defined as 4 bytes. The first byte is the number of sectors per track. The second byte is the number of sides. The next 2 bytes are a 16bit integer, sent in network byte order, signifying the number of tracks.

Note: Number of (sectors/sides/tracks) can be interchanged for the desired (sector/side/track) value, in the case of reading/writing to a disk.

The BIOS expects side and track to be indexed from 0, and sector to be indexed from 1.

Responses

reqstat = 0 for failure, or 1 for success. All other values are reserved.

Requests

There are currently 7 requests defined, their codes and functionality are as below.

REQ 0 - QUIT

This request should contain no data, and should be sent before closing the TCP connection. The server will then allow another connection. The server will not send a response packet to this, and is the only request to do so.

REQ 1 - GET DISK COUNT

This request should contain no data. The response should be 2 bytes in length. The first byte is equal to the number of floppy disks present, and the second byte is equal to the number of hard disks present.

REQ 2 - GET HARD DISK INFO

This request should contain 1 byte of data. This byte is equal to the drive number that is to be queried for information. The drive number should be indexed from 0, and should be less than the value returned from REQ 1.

The response will be 4 bytes, containing a CHS datatype. The values returned in the CHS will be total counts.

REQ 3 - READ DISK SECTOR

This request should contain 5 bytes of data. The first should contain the disk number. The next 4 should contain a CHS struct.

The disk number should be 0x00 for the 1st floppy, 0x01 for the 2nd floppy, 0x80 for the 1st hard drive, 0x81 for the 2nd hard drive... This is the value that will be passed to the BIOS.

The response will be 512 bytes, if successful, containing the sector data requested.

There is nothing in the protocol to stop you from trying to read beyond the length of whatever disk drive is installed. If the BIOS fails reading, however, this command will fail as well.

REQ 4 - WRITE DISK SECTOR

This request should contain 517 bytes of data. The first should contain the disk number. The next 4 should contain a CHS struct. The next 512 bytes will be the bytes to write to the sector.

The disk number should be 0x00 for the 1st floppy, 0x01 for the 2nd floppy, 0x80 for the 1st hard drive, 0x81 for the 2nd hard drive... This is the value that will be passed to the BIOS.

The response will contain no data.

There is nothing in the protocol to stop you from trying to write beyond the length of whatever disk drive is installed. If the BIOS fails writing, however, this command will fail as well.

REQ 5 - GET MAX DISK BUFFER SIZE

This request should contain no data. The response should be 2 bytes, interpreted as a 16 bit integer, sent in network byte order.

The response is equal to the maximum size of the disk buffer, and is the largest number of bytes that may be read/written to/from a drive using the READ/WRITE MULTIPLE DISK SECTORS commands.

Divide this number by 512 to obtain the maximum number of sectors you may request.

REQ 6 - READ MULTIPLE DISK SECTORS

This request should contain 6 bytes of data. The first should contain the disk number. The next 4 should contain a CHS struct. The last byte should contain the number of sectors to be read.

The response will be (sector count * 512 bytes), containing the sector data requested.

There is nothing in the protocol to stop you from trying to read beyond the length of whatever disk drive is installed. If the BIOS fails reading, however, this command will fail as well.

REQ 7 - WRITE MULTIPLE DISK SECTORS

This request should contain 6 + (sector count * 512) bytes of data. The first should contain the disk number. The next 4 should contain a CHS struct. The next byte is equal to the number of sectors to be written. The next (sector count * 512) bytes will be the bytes to write to the sectors.

There is nothing in the protocol to stop you from trying to write beyond the length of whatever disk drive is installed. If the BIOS fails writing, however, this command will fail as well.