[Qemu-devel] [Bug 659276] Re: Accessing Century byte via RTC

[Aurelien Jarno]

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.

** Changed in: qemu
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/659276

Title:
  Accessing Century byte via RTC

Status in QEMU:
  Invalid

Bug description:
  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