add directory study

study/sabre/os/files/Booting/CMOS_SEG.txt

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+From: James Vahn
+Subj: Cmos
+____________________________________________________________________________
+
+The standard AT CMOS addresses from 00h to 3Fh are easy,
+
+;    Read CMOS
+mov al,addr     ; 'addr' ranges from 00h to 3Fh.
+out 70h,al      ;  wakes up the port.
+jmp $+2         ;  a delay loop..
+in al,71h       ;  reads CMOS.
+
+;    Write CMOS
+mov al,addr     ; 'addr' ranges from 00h to 3Fh.
+out 70h,al      ;  wakes up the port.
+jmp $+2         ;  a delay loop..
+out 71h, value  ;  Writes 'value' from 00h to FFh.
+                ;    note that 'addr' 10h to 20h are checksummed.
+
+
+Some CMOS info...
+
+  addr        contents
+
+  00h         Seconds
+  01h         Second Alarm
+  02h         Minutes
+  03h         Minute Alarm
+  04h         Hours
+  05h         Hour Alarm
+  06h         Day of the Week
+  07h         Day of the Month
+  08h         Month
+  09h         Year
+  0Ah         Status Register A
+  0Bh         Status Register B
+  0Ch         Status Register C
+  0Dh         Status Register D
+  0Eh         Diagnostic Status Byte
+  0Fh         Shutdown Status Byte
+  10h         Disk Drive Type for Drives A: and B:
+              The drive-type bytes use bits 0:3 for the first
+              drive and 4:7 for the other disk drive types.
+  00h         no drive present
+  01h         double sided 360k
+  02h         high capacity (1.2 meg)
+  03h-0Fh     reserved
+  11h         (AT):Reserved    (PS/2):drive type for hard disk C:
+  12h         (PS/2):drive type for hard disk D:
+              (AT, XT/286):hard disk type for drives C: and D:
+  Format of drive-type entry for AT, XT/286:
+  0       number of cyls in drive (0-1023 allowed)
+  2       number of heads per drive (0-15 allowed)
+  3       starting reduced write compensation (not used on AT)
+  5       starting cylinder for write compensation
+  7       max. ECC data burst length, XT only
+  8       control byte
+  Bit
+  7       disable disk-access retries
+  6       disable ECC retries
+  5-4     reserved, set to zero
+  3       more than 8 heads
+  2-0     drive option on XT (not used by AT)
+  9       timeout value for XT (not used by AT)
+  12      landing zone cylinder number
+  14      number of sectors per track (default 17, 0-17 allowed)
+  13h         Reserved
+  14h         Equipment Byte (corresponds to sw. 1 on PC and XT)
+  15h-16h     Base Memory Size      (low,high)
+  17h-18h     Expansion Memory Size (low,high)
+  19h-20h     Reserved
+          (PS/2) POS information Model 50 (60 and 80 use a 2k
+          CMOS RAM that is not accessible through software)
+  21h-2Dh     Reserved (not checksumed)
+  2Eh-2Fh     Checksum of Bytes 10 Through 20  (low,high)
+  30h-31h     Exp. Memory Size as Det. by POST (low,high)
+  32h         Date Century Byte
+  33h         Information Flags (set during power-on)
+  34h-3Fh     Reserved - Put Your Name Here.