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8.1.3.2: Overview

To support some new features, I added new flag bits to the minor device number. These are (see zftape.h)(1):

#define ZFTAPE_Q80_MODE 8 (= bit 3) #define ZFTAPE_ZIP_MODE 16 (= bit 4) #define ZFTAPE_RAW_MODE 32 (= bit 5)

Already present in Bas Laarhoven's original ftape was bit 2, indicating the non-rewind mode (see Rewinding and non-rewinding devices) of the driver, and the meaning of the first two bits that indicate the drive selection mode (see Drive selection) of the tape drive(2).

The actual minor-device number is simply computed by a bitwise `or' of the bits that correspond to the desired features. A non rewinding device with compression, for example, has the following minor device number (drive selection method A):

  ZFTAPE_ZIP_MODE | FTAPE_NO_REWIND | ZFTAPE_SELECT_A
=       16        |        4        |         0 
= 0x14 = 20

The ZFTAPE_ZIP_MODE bit cannot be used in conjunction with the ZFTAPE_RAW_MODE bit as the latter allows raw access to the driver only. It follows from the above that there are 24 different zftape devices.


(1) The meaning of the ZFTAPE_Q80_MODE bit has changed from version 1.02 to version 1.03. To be more precise, this bit is meaningless now, it is just kept for compatibility reasons.

(2) there is in some sense support for use of multiple tape drives, but it is experimental and the two drives have to use different drive selection methods


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