# System Calls The system API is exposed to user code using the `COP` interrupt. The `C` accumulator is loaded with a function number; the other registers are loaded with call-specific data (or nothing), and any return values are placed in the same registers. What follows is a list of the system calls, their numbers, and register arguments they take, and what if any values they return. The system API is based loosely on, but not compatible with, that of CP/M-3 and MSX-DOS 2. Most calls return a status code in C. This code has one value, `STATUS_OK`, (equal to `0x0000`) which applies to all sxuch calls; this value indicates that the call was successful. Any other value will indicate some specific error. ## `0x00`: Terminate with Error Code Arguments: - `C`: `0x00` - `X`: Error code Return Values: - This call does not return. This call exits the calling program, setting the exit status code for the system on its way out. Program control will be returned to the command shell. ## `0x01`: Console Input Arguments: - `C`: `0x01` Return Values: - `C`: Character read from stdin This call reads one character from standard input. If there is no character ready, this call waits until there is one. The read character will also be echoed to the screen, just as if it had been passed to the Console Output call. This call traps certain sequences of characters for "terminal control" purposes. When this call traps such a character, it outputs nothing an continues waiting for another character to be ready. ## `0x02`: Console Output Arguments: - `C`: `0x02` - `X`: Character to output Return Values: - None This call sends a single chracter to the standard output, which is usually the terminal emulator. The character will be parsed by the terminal emulator to handle control characters and escape sequences. ## `0x03`: Direct Console Input Arguments: - `C`: `0x03` Return Values: - `C`: Character value or `NULL` This call does direct (raw) console input; if there is a character ready, it will be read, and if not, `NULL` will be returned. ## `0x04`: Direct Console Output Arguments: - `C`: `0x04` - `X`: Character value Return Values: - None This call does direct (raw) console output; the value supplied will be treated as the value to write to screen memory, and will not be interpreted for terminal control. ## `0x05`: String Output Arguments: - `C`: `0x05` - `X`: Bank of string - `Y`: Address of string Return Values: - None This call uses the 0x02 call "Console Output" above to send a `NULL`-terminated string to stdout. ## `0x06`: Buffered Line Input Arguments: - `C`: `0x06` - `X`: Bank of buffer - `Y`: Address of buffer Return values: - `C`: Status code This call will read up to 255 characters from stdin, or up to the first newline, whichever comes first. While taking input, a simple line editor is presented to the user. When the 255th character has been entered into the buffer, any further input will be ignored until a newline is entered. The newline in the resulting buffer will be replaced with a `NULL` to terminate the string. ## `0x07`: Console Status Arguments: - `C`: `0x07` Return Values: - `C`: Status Code This call checks stdin for a character to read. If there is none, this call will return zero in C; if there is a character ready, it will return nonzero in C. ## `0x08`: Return Version Number Arguments: - `C`: `0x08` Return Values: - `C`: Major version - `X`: Minor version - `Y`: Micro version This call returns the version number of the kernel. ## `0x09`: Get Date Arguments: - `C`: `0x09` - `X`: Bank of buffer - `Y`: Address of buffer Return Values: - None This call fills in the specified buffer with the current date, in the following format: ``` struct { uint16_t year // Current year uint8_t month; // 1 = January..12 = December uint8_t day; // 1..31 uint8_t weekday; // 0 = Sunday..6=Saturday } ``` ## `0x0A`: Set Date Arguments: - `C`: `0x0A` - `X`: Bank of buffer - `Y`: Address of buffer Return Values: - `C`: Status code Argument Structure: ``` struct { uint16_t year // Current year uint8_t month; // 1 = January..12 = December uint8_t day; // 1..31 uint8_t weekday; // 0 = Sunday..6=Saturday }; ``` This call sets the system date from the data in the argument structure. ## `0x0B`: Get Time Arguments: - `C`: `0x0B` - `X`: Bank of buffer - `Y`: Address of buffer Return Values: - `C`: Status code Argument Structure: ``` struct { uint8_t hour; // 0..23 uint8_t minute; // 0..59 uint8_t second; // 0..59 }; ``` This call fills in the specified argument structure with the current time. ## `0x0C`: Set Time Arguments: - `C`: `0x0C` - `X`: Bank of argument structure - `Y`: Address of argument structure Return Values: - `C`: Status code Argument Structure: ``` struct { uint8_t hour; // 0..23 uint8_t minute; // 0..59 uint8_t second; // 0..59 }; ``` This call sets the current time from the provided argument structure. ## `0x0D`: Open File Arguments: - `C`: `0x0D` - `X`: Bank of pathname string - `Y`: Address of pathname string Return Values: - `C`: Status code - `X`: File handle This call attempts to open the file referred to by the provided `NULL`-terminated string, which must contain a fully-qualified pathname -- something of the form `[drive]:/[dir]/[dir2]/filename.ext`, such as `sd0:/games/kaboom/readme.ansi`. If the file is successfully opened, `C` will contain `STATUS_OK`, and the `X` register will contain the file handle. On error, `C` will contain a negative value indicating which error has occured. ## `0x0E`: Close File Handle Arguments: - `C`: `0x0E` - `X`: File handle Return Values: - `C`: Status code This call attempts to close the file referred to by the provided file handle. On success, `C` will contain a status code of `STATUS_OK`. On error, `C` will contain a negative value, indicating an error has occured. ## `0x0F`: Duplicate File Handle Arguments: - `C`: `0x0F` - `X`: File handle Return Values: - `C`: Status code - `X`: Duplicate of file handle This call attempts to duplicate the provided file handle. The new file handle will be exactly identical to the provided one, and either may be used at any time. On success, `C` will contain a status code of `STATUS_OK`, and the `X` register will contain the duplicate file handle. On error, `C` will contain a negative value, indicating an error has occured. ## `0x10`: Read from File Arguments: - `C`: `0x10` - `X`: Bank of argument block - `Y`: Address of argument block Return Values: - `C`: Status code - `X`: Number of bytes actually read Argument Structure: ``` struct { void *dest; // Pointer to the buffer to use. uint16_t file; // File handle. size_t length; // Maximum number of bytes to read. }; ``` This call attempts to read up to `length` bytes from the file handle `file`, into the buffer pointed to by `dest`. On success, `C` will contain `STATUS_OK`, and the `X` register will contain the number of bytes actually read. On error, the C accumulator will contain a negative value indicating the specific error, and the `X` register will contain the number of bytes actually read. ## `0x11`: Write to File Arguments: - `C`: `0x11` - `X`: Bank of argument block - `Y`: Address of argument block Return Values: - `C`: Status code - `X`: Number of bytes actually written Argument Structure: ``` struct { void *src; // Pointer to the buffer to use. uint16_t file; // File handle. size_t length; // Maximum number of bytes to write. }; ``` This call attempts to write up to `length` bytes to the file handle `file`, from the buffer pointed to by `src`. On success, `C` will contain `STATUS_OK`, and the `X` register will contain the number of bytes actually written. On error, the C accumulator will contain a negative value indicating the specific error, and the `X` register will contain the number of bytes actually written. ## `0x12`: Seek in File Arguments: - `C`: `0x12` - `X`: Seek value - `Y`: Seek origin - `0x00`: Seek relative to the beginning of the file - `0x01`: Seek relative to the current position in the file - `0x02`: Seek relative to the end of the file Return value: - `C`: Status code - `X`: New file position (Low word) - `Y`: New file position (High word) This call moves the internal file pointer, the position in the specified file from which data can be read or to which data can be written. On success, this call returns `STATUS_OK` in `C`, and the new file position in `X` and `Y`. On error, `C` will contain a negative value indicating the specific error, and the new file position in `X` and `Y`. ## `0x13`: Device I/O Control This call performs driver-specific functions. ## `0x14`: Delete File Arguments: - `C`: `0x14` - `X`: Bank of pathname - `Y`: Address of pathname Return Values: - `C`: Status code This call attempts to delete the file indicated by the given `NULL`-terminated string, which must contain a fully-qualified pathname. On success, this `C` will contain `STATUS_OK`. On failure, `C` will contain a negative number indicating the specific error. ## `0x15`: Move File Arguments: - `C`: `0x15` - `X`: Bank of argument structure - `Y`: Address of argument structure Return Values: - `C`: Status code Argument Structure: ``` struct { char *src; // Fully-qualified source pathname. char *dest; // Fully-qualified destination pathname. }; ``` This call attempts to move or rename the specified `source` file to `dest`. On success, `C` will contain `STATUS_OK`. On error, `C` will contain a negative value indicating the specific error. ## `0x16`: Set File Attributes Arguments: - `C`: `0x16` - `X`: File handle - `Y`: File attribute bitmask Return Values: - `C`: Status code This call alters the file attributes of the specified file. The `Y` register should contain the result of a bitwise OR operation on any or all of the following values: - `FILE_READ_ONLY` - `FILE_HIDDEN` - `FILE_SYSTEM` - `FILE_ARCHIVE` Passing `0x0000` in the `Y` register will clear all attributes. ## `0x17`: Get Current Directory Arguments: - `C`: `0x17` - `X`: Bank of string - `Y`: Address of string Return Values: - `C`: Status code Argument Structure: ``` struct { char *drive; // The volume name of the drive to check char *dest; // Buffer for the returned directory path }; ``` This call attempts to create a `NULL`-terminated string with the path of the current directory in the drive with the volume name specified in the `drive` argument, and puts that string into the buffer pointed to by `dest`. On success, `C` will contain `STATUS_OK`. On failure, `C` will containe a negative value indicating the error type. ## `0x18`: Set Current Directory Arguments: - `C`: `0x18` - `X`: Bank of string - `Y`: Address of string Return Values: - `C`: Status code This call attempts to change the current directory on a the drive specified in the supplied `NULL`-terminated string to the directory listed in that string. On success, `C` will contain `STATUS_OK`. On failure, `C` will containe a negative value indicating the error type. ## `0x19`: Assign Device Alias Arguments: - `C`: `0x19` - `X`: Bank of argument structure - `Y`: Address of argument structure Return Values: - `C`: Status code Argument Structure: ``` struct { char *device; // The name of the device to alias char *alias; // The alias to assign to it }; ``` Device drivers in 65X-DOS identify themselves to the kernel by means of their "major number" -- the index into the internal device driver table at which the device driver's address can be found. Specific devices managed by a driver are distinguished from each other by "minor number" -- an arbitrary number which holds meaning only to the driver. Each device driver in 65X-DOS registers one or more major/minor number pairs to one or more "default" names. These aliases are what appear in a fully qualified pathname for a file before the `:` separator character. You might compare this to a "drive letter" in MS-DOS type systems, or to entries in the `/dev` directory on a Unix-like system. For example, the SD card driver might register the device name `sd0` for the first SD card. Drivers which do not expose file-like functionality still expose default names, because they use the `ioctl` interface to control their settings. This call attempts to add a secondary name to an existing device. This alias will work exactly like the default name, which will still be valid. A device can have any number of aliases assigned to it. These aliases are strings which contain any character except `NULL` or `:`. This call will fail if the `device` argument is not an exact match to any device alias, or if the `alias` argument value is already in use as a device alias. On success, `C` will contain `STATUS_OK`. On error, `C` will contain a negative value which indicates the specific error type. ## `0x1A`: Get Environment Variable Arguments: - `C`: `0x1A` - `X`: Bank of argument structure - `Y`: Address of argument structure Return Values: - `C`: Status code Argument Structure: ``` struct { char *name; // The name of the variable to read char *value; // Buffer for the value of the variable }; ``` This call gets the value of an environment variable specified by the `name` field of the argument structure, and copies it into the buffer pointed to by the `value` field. If the variable is not set, the value will be set to `NULL`, and the status code will be `ERR_ENV_UNSET`; otherwise the status code will be `STATUS_OK`. ## `0x1B`: Set Environment Variable Arguments: - `C`: `0x1A` - `X`: Bank of argument structure - `Y`: Address of argument structure Return Values: - `C`: Status code Argument Structure: ``` struct { char *name; // The name of the variable to set char *value; // Buffer for the new value of the variable }; ``` This call sets the value of an environment variable specified by the `name` field of the argument structure by copying the string pointed to by the `value` field. To unset a variable, pass `NULL` in the `value` field. This call always returns `STATUS_OK`.