This overview document presents the rou2exOS (aka r2) kernel interface for external applications. Applications should utilize custom programming language libraries provided in the apps repository and statically link them with their source code. Examples on how to use such libraries, how to compile them and link them are provided in directories named by concerned languages.

The privilege levels are to be specified and defined in the Global Descriptor Table (GDT) in early boot sequence procedures.

*Kernel itself handles multiple software (CPU exceptions) and hardware interrupts (e.g. IRQs).

All common interrupts are callable from anywhere, but are handled only when called from the defined CPU ring, therefore are locked to such space.

The system call (syscall) is a procedure for requesting or modifying of kernel components, modules and drivers. Syscalls use the software interrupts (int 0x7f) under the hood to notify the CPU and kernel to take an action. Parameters of a syscall are passed using the CPU registers that are listed below.

Please note that all values passed into a syscall must be aligned to 8 bytes (64bit).

Please note that these lists are incomplete as listed syscalls have to be implemented in the kernel ABI. To be expanded.

pub struct SysInfo {
    pub system_name: [u8; 32],
    pub system_user: [u8; 32],
    pub system_path: [u8; 32],
    pub system_version: [u8; 8],
    pub system_path_cluster: u32,
    pub system_uptime: u32,
}

typedef struct {
    uint8_t system_name[32];
    uint8_t system_user[32];
    uint8_t system_path[32];
    uint8_t system_version[8];
    uint32_t system_path_cluster;
    uint32_t  system_uptime;
} __attribute__((packed)) SysInfo_T;

#[repr(C, packed)]
pub struct RTC {
    pub seconds: u8,
    pub minutes: u8,
    pub hours: u8,
    pub day: u8,
    pub month: u8,
    pub year: u16,
}

typedef struct {
    uint8_t seconds;
    uint8_t minutes;
    uint8_t hours;
    uint8_t day;
    uint8_t month;
    uint16_t year;
} __attribute__((packed)) RTC_T;

#[repr(C, packed)]
#[derive(Default,Copy,Clone)]
pub struct Entry {
    pub name: [u8; 8],
    pub ext: [u8; 3],
    pub attr: u8,
    pub reserved: u8,
    pub create_time_tenths: u8,
    pub create_time: u16,
    pub create_date: u16,
    pub last_access_date: u16,
    pub high_cluster: u16,
    pub write_time: u16,
    pub write_date: u16,
    pub start_cluster: u16,
    pub file_size: u32,
}

typedef struct {
    uint8_t name[8];
    uint8_t ext[3];
    uint8_t attr;
    uint8_t reserved;
    uint8_t tenths;
    uint16_t create_time;
    uint16_t create_date;
    uint16_t last_access_time;
    uint16_t high_cluster;
    uint16_t write_time;
    uint16_t write_date;
    uint16_t start_cluster;
    uint32_t file_size;
} __attribute__((packed)) Entry_T;