83 lines
2.8 KiB
C
83 lines
2.8 KiB
C
/****************************************************************************
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* include/nuttx/sensors/msxxxx_crc4.h
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. 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, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#ifndef __INCLUDE_NUTTX_SENSORS_MSXXXX_CRC4_H
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#define __INCLUDE_NUTTX_SENSORS_MSXXXX_CRC4_H
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/****************************************************************************
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* Public Function Prototypes
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****************************************************************************/
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/****************************************************************************
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* Name: ms58xx_crc
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*
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* Description:
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* Calculate the CRC.
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*
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****************************************************************************/
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static uint8_t msxxxx_crc4(FAR uint16_t *src,
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uint8_t crcndx,
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uint16_t crcmask)
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{
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uint16_t cnt;
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uint16_t n_rem; /* CRC remainder */
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uint16_t crc_read; /* Original value of the CRC */
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uint8_t n_bit;
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n_rem = 0x00;
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crc_read = src[crcndx]; /* Save read CRC */
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src[crcndx] &= ~crcmask; /* CRC byte is replaced by 0 */
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for (cnt = 0; cnt < 16; cnt++) /* Operation is performed on bytes */
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{
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if (cnt % 2 == 1)
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{
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n_rem ^= (uint16_t)((src[cnt >> 1]) & 0x00ff);
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}
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else
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{
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n_rem ^= (uint16_t)(src[cnt >> 1] >> 8);
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}
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for (n_bit = 8; n_bit > 0; n_bit--)
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{
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if (n_rem & (0x8000))
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{
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n_rem = (n_rem << 1) ^ 0x3000;
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}
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else
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{
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n_rem = (n_rem << 1);
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}
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}
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}
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n_rem = (0x000f & (n_rem >> 12)); /* Final 4-bit reminder is CRC code */
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src[crcndx] = crc_read; /* Restore the crc_read to its original place */
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return (n_rem ^ 0x00);
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}
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#endif /* __INCLUDE_NUTTX_SENSORS_MSXXXX_CRC4_H */
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