OSWORD &0E

OSWORD &0E (14): Read Real-Time clock

Summary

On entry:
 XY?0=function code
 XY?0=0+n use 7-bit BCD date block
 XY?0=8+n use 8-bit BCD date block
 XY?0=0  XY?0=8   Read as 25-character string
 XY?0=1  XY?0=9   Read as 7- or 8-byte BCD block
 XY?0=2  XY?0=10  Convert 7- or 8-byte BCD block at XY+1 to string
 XY?0=3           Read as 5-byte centisecond time
 XY?0=3           Read 25-character string from file server (ANFS 4.2x)
 XY?0=4           Read BCD clock value from file server (ANFS)
 XY?0=4           Return "hh:mm:ss DDD dd-mm-yy tt",CR
                  where tt is temperature. (I2C Control ROM)
 XY?0=5
 XY?0=6
 XY?0=7
On exit:
 XY?x=if subcall unsupported, control block unchanged
 XY?x=if subcall supported, control block modified

Calls

On entry:
 XY?0=0:   Return clock value as string
 XY?0=8:   Return clock value as string
On exit:
 XY+0..24:  CR-terminated string
            Note: some implementations do not return the CR, so the
            caller should manually add a CR with XY?24=13.

On entry:
 XY?0=1:  Return 7-byte BCD clock value
 XY?0=9:  Return 8-byte BCD clock value
On exit:
 XY+0..6:  7-byte BCD clock value
 XY+0..7:  8-byte BCD clock value

On entry:
 XY?0=2:  Convert 7-bit BCD to string
 XY+1..7:  7-byte BCD clock value
 XY?0=10: Convert 8-bit BCD to string
 XY+1..8:  8-byte BCD clock value
On exit:
 XY+0..24: CR-terminated string

On entry:
 XY?0=3:   Return 5-byte centisecond clock value
On exit:
 XY?0..4:  Number of centiseconds since 00:00:00 01-Jan-1900

On entry:
 XY?0=3:  Return clock value as string from file server (ANFS 4.2x)
On exit:
 XY+0..24: CR-terminated string

On entry:
 XY?0=4:  Return BCD clock value from file server (ANFS).
On exit:
 XY+0..6:  7-byte BCD clock value

On entry:
 XY?0=4:  Return time, date and temperature string (I2C).
On exit:
 XY+0..24: CR-terminated string

Data format

The date string format is "DDD,dd mmm yyyy.hh:mm:ss". The punctuation is normally
irrelevant, the position of the component values is fixed.

The I2C temperature string format is "hh:mm:ss DDD dd-mm-yy tt" where tt is the
temperature.

7-byte BCD date block format:
 +0 year    &00-&99 year is 1980-2079
 +1 month   &01-&12
 +2 date    &01-&31
 +3 day     &01-&07 Sun-Sat or &00 for unsupported
 +4 hour    &00-&23
 +5 minute  &00-&59
 +6 second  &00-&59

8-byte BCD date block format:
 +0 century &00-&99
 +1 year    &00-&99
 +2 month   &01-&12
 +3 date    &01-&31
 +4 day     &01-&07 Sun-Sat or &00 for unsupported
 +5 hour    &00-&23
 +6 minute  &00-&59
 +7 second  &00-&59

3-byte BCD alarm block format:
 +0 hour    &00-&23 or &C0-&FF for 'any'
 +1 minute  &00-&59 or &C0-&FF for 'any'
 +2 second  &00-&59 or &C0-&FF for 'any'

Calling from BASIC

REM X%=>control block, Y%=X%DIV256
:
REM Read string:
?X%=0:A%=14:CALL OSWORD:IF ?X%=0 THEN T$="" ELSE X%?24=13:T$=$X%
:
REM Read BCD:
!X%=1:A%=14:CALL OSWORD:IF !X%=1 THEN unsupported ELSE data returned

Implementation

On a system without a Real Time Clock, the MOS passes OSWORD 14 to sideways ROMs for support.

Master MOS

The Master MOS 3 and MOS 4 implements subcalls 0,1,2. Unsupported subcodes are silently swallowed and not passed on. Unpatched versions always consistantly return the year in the date string as 19xx.

Master Compact

The Master MOS 5 implements subcall 2 to convert a BCD block to a string. It passes all other calls to sideways ROMs. If there is no response for subcall 0 and 1 it returns a default value of 31 Dec 1999, 23:59:59.

ANFS

Master ANFS 4.2x implements subcalls 0,1,3,4 and calls OSWORD 14,2 to convert the result of subcall 0 and 3 to a string. BBC ANFS 4.0x and 4.1x only implements subcall 4.

The ANFS implementation fails in a predictable manner with dates after 1996. The returned date is ((year-1981) DIV 16)*16+date and the returned year is (year-1981) AND 15. The date can be repaired across the whole date range with:

 date =BCDtoBIN(returned_date) AND 31
 month=BCDtoBIN(returned_month)
 year =(BCDtoBIN(returned_date) AND &E0) DIV 2 + BCDtoBIN(returned-year)+1900

SoftRTC

The SoftRTC module stores the time and date with the system TIME timer. It implements subcalls 0,1,2 and 8,9,10. The SoftRTC module included in HADFS only implements subcalls 0,1,2 with the date set with *SETDATE.

PMS Clock ROM

PMS Clock implements subcalls 0,1,2.

I2C Control ROM

The I2C Control ROM implements subcode 4 (clashing with ANFS).

TicToc ROM

TicToc returns a 24-byte time&date string from every call to OSWORD &14, completely ignoring the subcode.

RISC OS

Implements subcodes 0,1,2,3. Subcode 3 clashes with ANFS. The returned century is that set in the system configuration.

Notes

Several implementations implement clashing subcodes.

Y2K Issues

Some RTC systems always consistantly return the year in the date string as 19xx. This can be repaired with:

 Read time string to T$
 IF MID$(T$,14,1)<"8":T$=LEFT$(T$,11)+"20"+MID$(T$,14)

See Also

• OSWORD &0F
• https://mdfs.net/Docs/Comp/BBC/Osword/RTCOswords

Jgharston 12:56, 26 May 2009 (UTC) Jgharston (talk) 06:45, 12 April 2020 (CEST) Jgharston (talk) 23:56, 6 January 2023 (CET)