OS_ScreenMode 2, mode enumeration format 1

Hi,

while experimenting with screen mode enumeration, I have noticed some differences with the specs (IOMD build OS 5.22, PI3 build OS 5.23 from 07 Oct 2016).

Here is some extract from a log I produce on OS 5.22:
Modes (1024, 768) flags 0 log2bpp 3 ncolour 1
Modes (1024, 768) flags 0 log2bpp 4 ncolour 4095
Modes (1024, 768) flags 0 log2bpp 4 ncolour 63
Modes (1024, 768) flags 80 log2bpp 4 ncolour 65535
Modes (1024, 768) flags 0 log2bpp 5 ncolour 127

And this is from OS 5.23 on the PI:
Modes (1920, 1080) flags 0 log2bpp 3 ncolour 1
Modes (1920, 1080) flags 4080 log2bpp 4 ncolour 65535
Modes (1920, 1080) flags 0 log2bpp 5 ncolour 127

As you can see anything except for 4K & 64K modes has an incorrect ncolour value compared to the specs Valid Mode Variable Combinations

I’m not seeing anything unusual here (5.22 on Iyonix + IOMD).

Remember that there each mode could appear in one of two formats, the old format which doesn’t specify the mode flags/ncolour and the new format which does. So possibly it’s a bug in your code which is generating the missing values?

SYS "OS_ScreenMode",2 TO ,,,,,,,size%
size%=-size%
DIM block% size%
SYS "OS_ScreenMode",2,,,,,,block%,size% TO ,,count%
count%=-count%
PRINT count%;" modes in ";size%;" bytes"
WHILE count%>0
  count%-=1
  CASE block%?4 OF
    WHEN 1:
      PRINT "X";block%!8;" Y";block%!12;" depth ";block%!16;" rate ";block%!20;" name ";FNname(block%+24)
    WHEN 3:
      PRINT "X";block%!8;" Y";block%!12;" ncolour ";block%!16;" flags ";STR$~(block%!20);" log2bpp ";block%!24;" rate ";block%!28;" name ";FNname(block%+32)
    OTHERWISE:
      PRINT "Unknown format ";block%?4
  ENDCASE
  block% += block%!0
ENDWHILE
END

DEF FNname(a%)
A$=""
WHILE a%?0 > 0
  A$ += CHR$(a%?0)
  a%+=1
ENDWHILE
=A$

Correct, it’s a bug in the code for the parts of the list using the old format. ncolours = (1 << (2^log2bpp)) – 1, except of course in C “^” is EOR not exponent like in BASIC. Took me forever to notice it.