This commit allows STM32U5 devices to operate at 160 MHz.
On STM32U5, MSIS can run at 48 MHz and HSE can reach 50 MHz. Faster
clocks require using PLL1's R output, though PLL1 can serve other
functions besides using the R output for the system clock. This commit
extracts a public `PllConfig` struct, primarily to place associated
constructors on that type, but also with an eye towards enabling the P
and Q outputs in a later commit.
STM32U5 PLLs have various frequency requirements on each stage: after
the `m` prescaler, after the `n` multiplier, and after the `r` divider.
This commit implements the associated checks as assertions.
This commit fixes clock calculation and PLL register configuration
errors in PLL initialization.
STM32U5 has a PWR peripheral which can be configured to push Vcore into
different voltage ranges. System clocks exceeding 55 MHz require range
2, and system clocks exceeding 110 MHz require range 1. This commit
adds `voltage_range` to `Config` and configures PWR as directed.
The voltage range implies different performance limits on various clock
signals, including inside a PLL. This commit implements voltage range
<-> frequency range checks as assertions, and extracts the
otherwise-repeated MSIS, HSI16, and HSE initialization into private
methods on `Config`.
STM32U5 frequencies above 55 MHz require using the PWR EPOD booster.
The EPOD booster requires configuring a second `m` term for PLL1,
`mboost`, such that it falls in a particular range. (Recall that >50
MHz cannot be reached without PLL1, so there is no scenario where EPOD
is needed but PLL1 is not.) This commit configures and enables the EPOD
booster automatically as required.
The example spins too fast so it doesn't appear to change;
it's delaying for microseconds instead of milliseconds.
This commit slows it down and adds a comment noting the pin
mapping for the Adafruit feather rp2040+RFM95 LoRA module,
which has its Neopixel on pin 4 instead of 16.
