mirror of https://github.com/efabless/caravel.git
31 lines
1.2 KiB
ReStructuredText
31 lines
1.2 KiB
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.. raw:: html
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<!---
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# SPDX-FileCopyrightText: 2020 Efabless Corporation
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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# SPDX-License-Identifier: Apache-2.0
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-->
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External clock
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==============
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The external clock is provided to :ref:`clock <clock>` pin (C9).
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The external clock functions as the source clock for the entire processor.
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On startup, the processor runs at the same rate as the external clock.
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The processor program may access the :doc:`housekeeping-spi` to set the processor into PLL mode or DCO free-running mode.
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In PLL mode, the external clock is multiplied by the feedback divider value to obtain the core clock.
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In DCO mode, the processor is driven by a trimmed free-running ring oscillator.
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