pcfrtc(4) - NetBSD Manual Pages

PCFRTC                               LOCAL                              PCFRTC


NAME

     pcfrtc -- Driver for NPX PCF8583 Real-Time Clock and Calendar/Counter/240
     x 8bit RAM via I2C bus


SYNOPSIS

     pcfrtc* at iic? addr 0x50
     pcfrtc* at iic? addr 0x50 flags x
     pcfrtc* at iic? addr 0x51
     pcfrtc* at iic? addr 0x51 flags x


DESCRIPTION

     The pcfrtc driver supports the PCF8583 multifunction chip which can oper-
     ate in one of four modes depending on the value of the flag [if speci-
     fied]:

     mode 0 - Clock & Calendar using a 32768 hz crystal.
                   This is the default mode in the absence of a flags field
                   and is the state when a power-on reset occurs.

     mode 1 - Clock & Calendar using external 50 Hz clock.
                   Similar to mode 0, but relies on an external clock source
                   rather than a crystal.

     mode 2 - Counter for external inputs.
                   The clock & calendar are disabled and the device counts
                   external events using a 3 byte bcd counter [0-999999].

     mode 3 - Test mode.
                   This is undocumented and unlikely to be useful.

     The pcfrtc driver is commonly used to support a real-time clock using a
     32768 hz crystal and a backup battery.  It also provides a small amount
     of battery backed RAM which is used, for example, for bootstrapping
     acorn32 system.  It is possible to use an external 50hz clock by switch-
     ing to mode 1 -- this might be useful with a European mains derived sig-
     nal as the long term drift is likely to be less than an unstabilised
     crystal.  Access methods to retrieve and set date and time are provided
     through the TODR interface defined in todr(9).

     Switching to mode 2 provides access to a 6 digit BCD counter, which can
     be used to count arbitary external events.  The driver maps this counter
     to an integer envstat variable, which can be read via the normal envstat
     subsystem, and also exposes a sysctl variable to allow the counter to be
     reset.


SYSCTL VARIABLES

     In mode 2 the following sysctl(3) variables are provided:

     hw.pcfrtc1.counter_reset
             If this is set to 1 then the next read of the envstat counter
             causes the BCD counter to be zeroed and resets the sysctl vari-
             able back to zero.


SEE ALSO

     todr(9), envstat(8), sysctl(8)


HISTORY

     The pcfrtc driver first appeared in NetBSD 1.0.


AUTHORS

     The pcfrtc driver was written by Steve C. Woodford and
     Jason R. Thorpe for Wasabi Systems, Inc. based on Ben Harris's PCF8583
     driver for NetBSD/acorn26.

     Subsequent modifications to support other modes by
     Dave Tyson <dtyson@anduin.org.uk>


BUGS

     The driver does not support the chip's alarm and timer features.

NetBSD 11.99                    October 1, 2026                   NetBSD 11.99