[MiNT] Launching MiNT from a DOS FAT partition

["Roger Burrows" <rfburrows@ymail.com>]

Mark Duckworth reported a problem on the ACP forum when trying to launch MiNT 
from a DOS FAT partition under EmuTOS.  MiNT did not boot, because the startup 
code refused to login his big DOS-style FAT partitions.  Looking at the 
relevant MiNT code, I see that MiNT's FATFS will not login a drive where the 
cluster size in bytes is bigger than cache.max_size.  In init_block_IO(), 
cache.max_size is calculated as:
	max(MIN_BLOCK,2*max_sect_siz)
where MIN_BLOCK is 8192, and max_sect_siz is taken from the AHDI pun_info 
structure, where it is the maximum logical sector size on any of the host's 
drives.  For a system with only DOS-style partitions, this will be 512 bytes.

So if you try to run MiNT from EmuTOS running on a DOS-style partition, 
max_sect_siz will be set to 512, and thus cache.max_size to 8192.  Accessing a 
partition with clusters larger than 8192 bytes (i.e. a partition larger than 
512MB) is not possible, so MiNT will not start.

I'm not sure where the fix should be: perhaps MIN_BLOCK should be 32768?

Roger
P.S. This isn't a problem with FireTOS, since it lies about max_sect_siz, but I 
don't think EmuTOS should be lying too.