Re: question about CHECK_VALUE for PCGI_UT->LU->exists

Thu Feb 19 2004, Yi-Shin Li wrote:
> Please help clarify the following comment from line# 1768 to 1779 of 
> ifo_read.c,
> ifoRead_PGCI_UT(ifo_handle_t *ifofile):
> 
>  for(i = 0; i < pgci_ut->nr_of_lus; i++) {
>    // Maybe this is only defined for v1.1 and later titles?
>    /* If the bits in 'lu[i].exists' are enumerated abcd efgh then:
>            VTS_x_yy.IFO        VIDEO_TS.IFO
>       a == 0x83 "Root"         0x82 "Title"
>       b == 0x84 "Subpicture"
>       c == 0x85 "Audio"
>       d == 0x86 "Angle"
>       e == 0x87 "PTT"
>    */
>    CHECK_VALUE((pgci_ut->lu[i].exists & 0x07) == 0);
>  }
> 

  LU_SRP #1 - #LU_Ns  Language Unit Search Pointer
    for(n=0, m=8; n < number of PGCI_LUs; n++, m+=8) {
      [(m+0)-(m+1)]   Menu Language Code
      [(m+2)]         --
      [(m+3)]         Menu Existence mask
                       (VMGM Maks bits 'Ayyy yyyy': A == Title menu(2)
                        VTSM Mask bits 'ABCD Eyyy':
                        A == Root menu(3)  B == Sub-picture menu(4)
                        C == Audio menu(5) D == Angle menu(6)
                        E == PTT menu(7) )
 
      [(m+4)-(m+7)]   Language start byte
    }


  PGCI_SRP #1 - #PGCI_SRP_Ns  PGCI Search Pointer
    for(n=0, m=8; n < number of PGCI_SRP; n++, m+=8) {
      [(m+0)-(m_4)    PGCI Category
         [(m+0)]      PGC #(n+1)'s Category Menu mask bits 'Xyyy zzzz'
                       (X==entry, 0: not an entry PGC, 1: an entry PGC
                        VMGM zzzz==Menu ID, 0010: Title
                        VTSM zzzz==Menu ID, 0011: Root, 0100: subpic, etc.
                        VTS  yyyzzzz==VTS Title number)
      ...
The comment isn't very clear (perhaps even missplaced one could claim).
The 'exists' field is just a bit mask, where bit 'a' indicates the
existance (i.e. presens among the pgcs in this title set) of the "root" 
menu, that has code 3 (and sice menu pgcs are 'entry'  pgcs it has the
high bit set) so the entry_id byte (in pgic_srp_t) will be 0x83.
Also code is shared between VTSM and VMGM event though there are sligh
differences.

> Per http://dvd.sourceforge.net/dvdinfo/ifo_vmg.html#pgciut, the 
> pcgi_ut->lu[i].exists
> stands for "Menu existence flag", which is 0x80 for titles. It make 
> sence for the
> CHECK_VALUE statement.
> 
> However, if the comment above is *true*, the CHECK_VALUE will always 
> generate
> error messages. Am I right?
> 
No since the low bits i.e. fgh are unused, the CHECK_VALUE checks that
they are indeed always 0.  Most of these was just help for us during
development and debuging.

> I don't have a copy of DVD-VIDEO spec on my hand. So, I can't confirm this.
> Would anybody please clarify this question?     Thanks in advance!!
> 
Very few of us do... 
It would have helped us a lot when writing the code though ;-)

/Håkan