Driver parameters

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From the very first Elphel camera (Model 303) camera driver maintained data array that was accessible by the applications through IOCTL calls. Total number of elements (32-bit data words) was 64 (limited by address bits designated for that purpose in IOCTL command map, the indexes are defined in the c313a.h(names starting with P_ ). Most (but not all) of the elements are represented in two arrays - imageParamsW[] and imageParamsR[], first (W for "write") having the data passed by the applications through IOCTL (example from the ccam.c - described in Ccam.cgi. The next line passes compression quality received as part of the GET request to the driver:

1852         if ((vp=paramValue(gparams, "iq")))		ioctl(devfd, _CCCMD(CCAM_WPARS ,  P_QUALITY),      strtol (vp,&cp,10));

The second array - imageParamsR[] (R for "read") holds the current value that driver uses. In most cases driver tries to make this value as close as possible to the one specified by application, if the application passed the invalid value driver will use the corrected one. Next line returns the current image width used by the driver (currently it is always a multiple of 16):

1136    ImageWidth =  ioctl(data_fd, _CCCMD( CCAM_RPARS , P_ACTUAL_WIDTH ), 0);