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This patch adds HSE and PLL as a system clock oscillator for STM32L4. This allows us to drive the chip at a higher frequency (up to 80 MHz), which is necessary to big-bang GPIO ports accurately. BUG=none BRANCH=tot TEST=make buildall. Verified console works on STM32L476G-Eval using HSE, PLL-HSE, PLL-HSI, PLL-MSI as an oscillator. Verified console runs soundly with different frequencies from 20 Mhz to 80 Mhz. Verified frequencies using oscilloscope on MCO (Microcontroller Clock Output) port up to 50 MHz. Change-Id: I493cdb6c323eb4e6a1560f6d030935c1950b1a2a Reviewed-on: https://chromium-review.googlesource.com/341275 Commit-Ready: Daisuke Nojiri <dnojiri@chromium.org> Tested-by: Daisuke Nojiri <dnojiri@chromium.org> Reviewed-by: Randall Spangler <rspangler@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit For instructions on building from source, refer to http://www.chromium.org/chromium-os/ec-development/getting-started-building-ec-images-quickly