Basic Concepts
Figure 4.14: Device Management Functions
A device name is a string of up to 8 characters consisting of the following elements.
#define L_DEVNM 8 /* Device name length */
Type Name indicating the device type
Characters a to z and A to Z can be used.
Unit One letter indicating a physical device
Each unit is assigned a letter from a to z in order starting from a.
Subunit One to three digits indicating a logical device
Each subunit is assigned a number from 0 to 254 in order starting from 0.
Device names take the format type + unit + subunit. Some devices may not have a unit or subunit, in which case the corresponding field is omitted.
A name consisting of type + unit is called a physical device name. A name consisting of type + unit + subunit may be called a logical device name to distinguish it from a physical device name. If there is no subunit, the physical device name and logical device name are identical. The term “device name” by itself means the logical device name.
A subunit generally refers to a partition on a hard disk but can be used to mean other logical devices as well.
hda Hard disk (entire disk)
hda0 Hard disk (1st partition)
fda Floppy disk
rsa Serial port
kbpd Keyboard/pointing device
By registering a device (device driver) with µT-Kernel, a device ID (> 0) is assigned to the device (physical device name). Device IDs are assigned to each physical device. The device ID of a logical device consists of the device ID assigned to the physical device to which is appended the subunit number + 1 (1 to 255).
devid: The device ID assigned at device registration
devid Physical device
devid + n + 1 The nth subunit (logical device)
hda devid Entire hard disk
hda0 devid + 1 1st partition of hard disk
hda1 devid + 2 2nd partition of hard disk
Device attributes are defined as follows, in order to classify devices by their properties.
IIII IIII IIII IIII PRxx xxxx KKKK KKKK
The upper 16 bits are device-dependent attributes defined for each device.
The lower 16 bits are standard attributes defined as follows.
#define TD_PROTECT 0x8000 /* P: write protection */
#define TD_REMOVABLE 0x4000 /* R: removable media */
#define TD_DEVKIND 0x00ff /* K: device/media kind */
#define TD_DEVTYPE 0x00f0 /* device type */
/* device type */
#define TDK_UNDEF 0x0000 /* undefined/unknown */
#define TDK_DISK 0x0010 /* disk device */
/* disk kind */
#define TDK_DISK_UNDEF 0x0010 /* miscellaneous disk */
#define TDK_DISK_RAM 0x0011 /* RAM disk (used as main memory) */
#define TDK_DISK_ROM 0x0012 /* ROM disk (used as main memory) */
#define TDK_DISK_FLA 0x0013 /* Flash ROM or other silicon disk */
#define TDK_DISK_FD 0x0014 /* floppy disk */
#define TDK_DISK_HD 0x0015 /* hard disk */
#define TDK_DISK_CDROM 0x0016 /* CD-ROM */
Currently, no device types other than disks are defined. Other devices are assigned to undefined type (TDK_UNDEF). Note that device types are defined for the sake of distinguishing devices from the standpoint of the user as necessary, such as when applications must change their processing based on the type of device or media. Devices for which no such distinctions are necessary do not have to have a device type assigned. See the individual device driver specifications regarding device-dependent attributes.
A device descriptor (> 0) is an identifier used for accessing a device, assigned by µT-Kernel when a device is opened.
A device descriptor belongs to a resource group. Operations using a device descriptor can be performed only by tasks belonging to the same resource group as the device descriptor. Error code (E_OACV) is returned for requests from tasks belonging to a different resource group.
When an IO request is made to a device, a request ID (> 0) is assigned identifying the request. This ID can be used to wait for IO completion.
Device data is specified by a data number. Data is classified into device-specific data and attribute data as follows.
Device-specific data: Data number > 0
As device-specific data, the data numbers are defined separately for each device.
Examples
Disk Data number = physical block number
Serial port Data number = 0 only
Attribute data: Data number < 0
Attribute data specifies driver or device state acquisition and setting modes, and special functions, etc.
Data numbers common to devices are defined but device-dependent attribute data can also be defined. Details are given later.
The type of data number is W instead of INT.
Comments
Click here to Post a Comment