Accessing Century byte via RTC

[Ian Seyler]

With the RTC configure for Binary instead of BCD I am getting the incorrect result for Century.

 mov al, 0x0B ; Set RTC to binary mode
 out 0x70, al
 in al, 0x71
 bts ax, 2
 mov bl, al
 mov al, 0x0B
 out 0x70, al
 mov al, bl
 out 0x71, al

 mov al, 0x32 ; Century
 out 0x70, al
 in al, 0x71

In QEMU 0.12.5 it returns 0x20 but should return 0x14. The following work correctly:

 mov al, 0x09 ; Year
 out 0x70, al
 in al, 0x71

 mov al, 0x08 ; Month
 out 0x70, al
 in al, 0x71

 mov al, 0x07 ; Day
 out 0x70, al
 in al, 0x71

[Aurelien Jarno (aurel32)]

The century register is only present in "recent" version of the chip, and is at an address corresponding to the NVRAM memory. It is not manipulated directly by the RTC and therefore is always in BCD format. The current QEMU implementation is correct.