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747e902761
We now have the same API for MMIO and CPU registers. Makes the code more concise, inntuitive, and improves readability. https://crates.io/crates/register
41 lines
1.6 KiB
Markdown
41 lines
1.6 KiB
Markdown
# Tutorial 0A - Power management
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For embedded systems, power consumption is critical. The Raspberry Pi 3 has a
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very sophisticated PM interface. You can turn each device on and off
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independently. There's a catch though. The GPIO VCC pins are hardwired, there's
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no way to turn them off programmatically. This means if you connect some devices
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to them, you'll have to implement a way to turn those devices off (with a
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transistor connected to a data GPIO pin for example).
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## power.rs
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Unfortunately, the documentation about the PM interface is very very rare. We
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will therefore more or less implement a carbon copy of respective functions of
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Linux'
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[bcm2835_wdt.c](https://github.com/torvalds/linux/blob/master/drivers/watchdog/bcm2835_wdt.c)
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driver.
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The power management controller is one of the peripherals that are not emulated
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properly by QEMU. Our implementation therefore works on real hardware only.
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`Power::off(&self, mbox: &mut mbox::Mbox, gpio: &gpio::GPIO)` shuts down the
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board to an almost zero power consumption state.
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`Power::reset(&self)` reboots the machine. Also handled by the PMC, and since
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the Raspberry Pi does not have a hardware reset button, it's very useful.
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When using `make raspboot` and choosing `reset()`, you can see your code in
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action nicely as you generate a boot-loop.
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## gpio.rs
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We introduce a lot of new GPIO pins. It's a good time to refactor the GPIO MMIO
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interface into its own type with the common `RegisterBlock` implementation that
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you already know from the other components.
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## main.rs
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We display a simple menu, and wait for user input. Depending on the input, we
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reboot the system or power it off.
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