Int 21 Fn 2535  P - Phar Lap 386/dos-extender V3.0+ - Read/write System R  [E]

   AX = 2535h
   EBX = direction (00h read registers, 01h write)
   DS:EDX -> system register record (see #1063)

Return: CF clear

Note:  this call is only available under MS Windows if PHARLAP.386 VDD is
     installed

Format of Phar Lap system register record:
Offset Size    Description (Table 1063)
 00h   DWORD   CR0
 04h  4 DWORDs DR0,DR1,DR2,DR3
 14h  2 DWORDs reserved
 1Ch  2 DWORDs DR6,DR7
 24h  3 DWORDs reserved