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This combines a real-time clock and 31 bytes of battery-backed RAM in a single package. The driver can also be used with any other chips that provide the same interface to the clock hardware. The package will usually be loaded into the configuration automatically whenever selecting a target which contains a compatible chip. By default it will provide the standard eCos wallclock device, although another implementation such as software emulation may be selected if desired.
The only other configuration options related to this package allow users to change the compiler flags. If the application does not actually use the wallclock device, directly or indirectly, then the code should get removed automatically at link-time to ensure that the application does not suffer any unnecessary overheads. The functionality is not normally accessed directly.
Instead it is used by the C library time package to implement standard calls such as time and gmtime. In addition RedBoot provides a date command which interacts with the wallclock device. The offset specifies the starting address within the RAM and should be between 0 and The buffer provides the destination or source of the data, and the length gives the number of bytes transferred. Wrap-around is not supported so the sum of the offset and length should also be less than Applications should not call any wallclock-related functions nor any of the DSspecific functions before that constructor has run.
Porting The DS is accessed via a 3-wire bus. At the time of writing there is no generic 3-wire support package within eCos, so instead the wallclock driver expects to bit-bang some GPIO lines.
DS 3 of 14 X1, X2 — Connections for a standard The internal oscillator is designed for operation with a crystal having a specified load capacitance of 6 pF. In this configuration, the X1 pin is connected to the external oscillator signal and the X2 pin is floated. Each data transfer is initiated by a command byte. The MSB Bit 7 must be a logic 1. If it is 0, writes to the DS will be disabled. Bits 1 through 5 specify the designated registers to be input or output, and the LSB bit 0 specifies a write operation input if logic 0 or read operation output if logic 1.
DALLAS DS1302 PDF