35 lines
1.9 KiB
Markdown
35 lines
1.9 KiB
Markdown
# ProDOS Clock Drivers
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Other than the Apple IIgs model, the Apple II did not ship with a real-time system clock. Many third party [Apple II system clocks](https://en.wikipedia.org/wiki/Apple_II_system_clocks) were produced in the 1980s, and many new system clocks are available, either as entirely new designs or recreations.
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The ProDOS operating system for the Apple II personal computer line natively supports the Thunderclock real-time clock card, but there is a protocol for custom clock drivers to be installed:
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* Check `MACHID` bit 0 to see if a clock is already active; abort if so.
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* Optional: Probe hardware to determine if the clock is present; abort if not.
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* Relocate the clock driver to LC bank 1, at the address at `DATETIME`+1
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* Update `DATETIME` to be a `JMP` instruction.
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* Optional: Chain to the next `.SYSTEM` file.
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In addition:
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* The clock driver must fit into 125 bytes.
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* The driver may dirty $200-$207 but other memory must be restored if modified.
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* When invoked, the clock driver should read the clock hardware and encode the date and time into `DATELO`/`DATEHI` and `TIMELO`/`TIMEHI`.
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* ProDOS calls the clock driver when `GET_TIME` is called, and on every call (`CREATE`, `RENAME`, etc) that might need the date and time.
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See https://prodos8.com/docs/techref/adding-routines-to-prodos/ for more information.
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## Included drivers
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This directory includes drivers for the following real-time clocks:
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* [No-Slot Clock](https://www.reactivemicro.com/product/no-slot-clock/)
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* [ROMX Real-Time Clock](https://theromexchange.com/)
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* [FujiNet Clock](https://fujinet.online/)
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* DClock
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* Cricket!
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All follow the above protocol: install only if there is not already a clock, probe for the clock before installing, and chain to the next driver.
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In addition, the "jumbo" directory combines the other driver installers to create a single unified clock driver installer. See its [README](jumbo/README.md) for more details.
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