dpm.h File Reference

Packed on-disk structures of the Data Position Measurement (DPM) block. More...

#include <stdint.h>

Go to the source code of this file.

Data Structures
struct	DpmHeader
	Header of the Data Position Measurement block. More...
struct	DpmEntry
	A DPM control point. More...
struct	DpmCalibration
	A rotation calibration done while measuring. More...

Macros
#define	DPM_UNITS_PER_TURN   2560000
	Angle units per turn, Alcohol 120% units (256 per turn) multiplied by 10000.
#define	DPM_UNITS_PER_ALCOHOL_UNIT   10000
	Angle units per Alcohol 120% unit.
#define	DPM_FLAG_OPPOSITE_TRACK_PATH   0x01
	Bit set in DpmHeader::flags when the layers use opposite track path.

Typedefs
typedef struct DpmHeader	DpmHeader
typedef struct DpmEntry	DpmEntry
typedef struct DpmCalibration	DpmCalibration

Enumerations
enum	DpmEntryStatus {   DpmStatusUnknown = 0 , DpmStatusMeasured = 1 , DpmStatusRemeasured = 2 , DpmStatusInterpolated = 3 ,   DpmStatusUnreadable = 4 , DpmStatusLayerBreak = 5 }
	Status of the bin of sectors that ends at an entry. More...

Detailed Description

Packed on-disk structures of the Data Position Measurement (DPM) block.

Data Position Measurement records the physical angle of sectors along the spiral track of an optical disc, as measured by timing reads. The angle is cumulative: it starts at 0 on the first entry and grows by one full turn every DPM_UNITS_PER_TURN units, so it also counts how many times the disc turned.

Binary layout (little-endian, packed):

DpmHeader (sizeof = 40 bytes) uint64_t layerEnd[layerEnds] -> last sector of every layer but the last, increasing DpmEntry entry[entries] -> control points, strictly increasing sector DpmCalibration calibration[calibrations]

length = layerEnds * 8 + entries * sizeof(DpmEntry) + calibrations * sizeof(DpmCalibration) crc64 = CRC64-ECMA of the length bytes that follow the header

The density, in degrees per sector, of the bin between two consecutive entries is (angle[i + 1] - angle[i]) * 360 / DPM_UNITS_PER_TURN / (lba[i + 1] - lba[i]).

Alcohol 120% stores the same cumulative angle, in 256 units per turn, on a uniform grid. A value of this block divided by DPM_UNITS_PER_ALCOHOL_UNIT, rounded, is the Alcohol 120% value.

Warning

Structures are packed; never rely on natural alignment when mapping from a byte buffer.

Definition in file dpm.h.

Macro Definition Documentation

DPM_FLAG_OPPOSITE_TRACK_PATH

#define DPM_FLAG_OPPOSITE_TRACK_PATH   0x01

Bit set in DpmHeader::flags when the layers use opposite track path.

Definition at line 58 of file dpm.h.

DPM_UNITS_PER_ALCOHOL_UNIT

#define DPM_UNITS_PER_ALCOHOL_UNIT   10000

Angle units per Alcohol 120% unit.

Definition at line 55 of file dpm.h.

DPM_UNITS_PER_TURN

#define DPM_UNITS_PER_TURN   2560000

Angle units per turn, Alcohol 120% units (256 per turn) multiplied by 10000.

Definition at line 53 of file dpm.h.

Typedef Documentation

DpmCalibration

typedef struct DpmCalibration DpmCalibration

DpmEntry

typedef struct DpmEntry DpmEntry

DpmHeader

typedef struct DpmHeader DpmHeader

Enumeration Type Documentation

DpmEntryStatus

enum DpmEntryStatus

Status of the bin of sectors that ends at an entry.

Ignored for the first entry.

Enumerator
DpmStatusUnknown	Unknown, e.g. imported from a format that does not record it.
DpmStatusMeasured	Measured on the first attempt.
DpmStatusRemeasured	Measured again because the first measurement was an outlier.
DpmStatusInterpolated	Measurement failed, interpolated from its neighbours.
DpmStatusUnreadable	Sectors could not be read, interpolated from its neighbours.
DpmStatusLayerBreak	Bin crosses a layer boundary or is too short, density copied from the bin before.

Definition at line 63 of file dpm.h.