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Before entering STOP mode, we need to ensure UART Tx has completed. Otherwise, we may lose some characters or some bits within a character. For Tx DMA mode, this is already done as we wait until TC (Tx complete) is set before disabling Tx. However, when not using DMA, we enable sleep when TXE is set. At this moment, the last character is still in the shift register and going into sleep causes loss of the whole or part of the last character. To avoid this, let's enable TC interrupt and enable sleep only if we have no more characters to send and TC is set. BRANCH=None BUG=chrome-os-partner:33219 TEST=Enable low power mode on Ryu P2. Type when the EC is in STOP mode and check there is no broken character. Change-Id: Ife42671882b7f1d1d17734d7d20fb4ba7dffb371 Signed-off-by: Vic Yang <victoryang@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/225283 Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit