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47 lines
1.4 KiB
C
47 lines
1.4 KiB
C
/*
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* Copyright 2024 Google LLC
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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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#include "delay.h"
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#include "util/attributes.h"
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#include "stm32f7xx.h"
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#include <inttypes.h>
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void delay_us(uint32_t us) {
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// Empirically (measured on a C2 bb), 1 loop = 1 cycle. (sysclk @
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// 16MHz, I-Cache disabled) Alignment of code will have some impact on how
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// long this actually takes
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uint32_t delay_loops = us * 16;
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__asm volatile (
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"spinloop: \n"
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" subs %[delay_loops], #1 \n"
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" bne spinloop \n"
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: [delay_loops] "+r" (delay_loops) // read-write operand
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:
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: "cc"
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);
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}
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void delay_ms(uint32_t millis) {
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// delay_us(millis*1000) is not used because a long delay could easily
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// overflow the veriable. Without the outer loop, a delay of even five
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// seconds would overflow.
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while (millis--) {
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delay_us(1000);
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}
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}
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