| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| |
| #include "os/os_cputime.h" |
| |
| /** |
| * This module implements cputime functionality for timers for which: |
| * a. freq is a power of 2 Hz, and |
| * b. 256 Hz <= freq < 1 MHz |
| */ |
| |
| #if defined(OS_CPUTIME_FREQ_PWR2) |
| |
| /** |
| * @addtogroup OSKernel Operating System Kernel |
| * @{ |
| * @defgroup OSCPUTime High Resolution Timers |
| * @{ |
| */ |
| |
| /** |
| * os cputime usecs to ticks |
| * |
| * Converts the given number of microseconds into cputime ticks. |
| * |
| * @param usecs The number of microseconds to convert to ticks |
| * |
| * @return uint32_t The number of ticks corresponding to 'usecs' |
| */ |
| uint32_t |
| os_cputime_usecs_to_ticks(uint32_t usecs) |
| { |
| uint64_t ticks; |
| |
| /* |
| * Faster calculation but could be off 1 full tick since we do not |
| * add residual back. Adding back the residual is commented out below, but |
| * shown. |
| */ |
| ticks = (1ULL << 32) * MYNEWT_VAL(OS_CPUTIME_FREQ) / 1000000 * usecs; |
| |
| /* Residual for 32768 Hz. */ |
| //ticks += ((uint64_t)usecs * (1526122139+1)) >> 32; |
| |
| return ticks >> 32; |
| } |
| |
| /** |
| * cputime ticks to usecs |
| * |
| * Convert the given number of ticks into microseconds. |
| * |
| * @param ticks The number of ticks to convert to microseconds. |
| * |
| * @return uint32_t The number of microseconds corresponding to 'ticks' |
| * |
| * NOTE: This calculation will overflow if the value for ticks is greater |
| * than 140737488. I am not going to check that here because that many ticks |
| * is about 4222 seconds, way more than what this routine should be used for. |
| */ |
| uint32_t |
| os_cputime_ticks_to_usecs(uint32_t ticks) |
| { |
| uint32_t usecs; |
| uint32_t shift; |
| uint32_t freq; |
| |
| /* Given: `freq = 2^n`, calculate `n`. */ |
| /* Note: this looks like a lot of work, but gcc can optimize it away since |
| * `freq` is known at compile time. |
| */ |
| freq = MYNEWT_VAL(OS_CPUTIME_FREQ); |
| shift = 0; |
| while (freq != 0) { |
| freq >>= 1; |
| shift++; |
| } |
| |
| if (shift <= 7) { |
| return 0; |
| } |
| shift -= 7; |
| |
| usecs = ((ticks >> shift) * 15625) + (((ticks & 0x1ff) * 15625) >> shift); |
| return usecs; |
| } |
| |
| /** |
| * @} OSCPUTime |
| * @} OSKernel |
| */ |
| |
| #endif |
