Line data    Source code

       1            0 : /*
       2              :  * Copyright (c) 2021 Intel Corporation
       3              :  * SPDX-License-Identifier: Apache-2.0
       4              :  */
       5              : #ifndef ZEPHYR_INCLUDE_SYS_WINSTREAM_H_
       6              : #define ZEPHYR_INCLUDE_SYS_WINSTREAM_H_
       7              : 
       8              : #include <stdint.h>
       9              : 
      10              : /** @brief Lockless shared memory byte stream IPC
      11              :  *
      12              :  * The sys_winstream utility implements a unidirectional byte stream
      13              :  * with simple read/write semantics on top of a memory region shared
      14              :  * by the writer and reader.  It requires no locking or
      15              :  * synchronization mechanisms beyond reliable ordering of memory
      16              :  * operations, and so is a good fit for use with heterogeneous shared
      17              :  * memory environments (for example, where Zephyr needs to talk to
      18              :  * other CPUs in the system running their own software).
      19              :  *
      20              :  * This object does not keep track of the last sequence number read: the
      21              :  * reader must keep that state and provide it on every read
      22              :  * operation. After reaching "steady state", 'end' and 'start' are one
      23              :  * byte apart because the buffer is always full.
      24              :  */
      25            1 : struct sys_winstream {
      26            0 :         uint32_t len;   /* Length of data[] in bytes */
      27            0 :         uint32_t start; /* Index of first valid byte in data[] */
      28            0 :         uint32_t end;   /* Index of next byte in data[] to write */
      29            0 :         uint32_t seq;   /* Mod-2^32 index of 'end' since stream init */
      30            0 :         uint8_t data[];
      31              : };
      32              : 
      33              : /** @brief Construct a sys_winstream from a region of memory
      34              :  *
      35              :  * This function initializes a sys_winstream in an arbitrarily-sized
      36              :  * region of memory, returning the resulting object (which is
      37              :  * guaranteed to be at the same address as the buffer).  The memory
      38              :  * must (obviously) be shared between the reader and writer, and all
      39              :  * operations to it must be coherent and consistently ordered.
      40              :  *
      41              :  * @param buf Pointer to a region of memory to contain the stream
      42              :  * @param buflen Length of the buffer, must be large enough to contain
      43              :  *               the struct sys_winstream and at least one byte of
      44              :  *               data.
      45              :  * @return A pointer to an initialized sys_winstream (same address as
      46              :  *         the buf parameter).
      47              :  */
      48            1 : static inline struct sys_winstream *sys_winstream_init(void *buf, int buflen)
      49              : {
      50              :         struct sys_winstream *ws = buf, tmp = { .len = buflen - sizeof(*ws) };
      51              : 
      52              :         *ws = tmp;
      53              :         return ws;
      54              : }
      55              : 
      56              : /** @brief Write bytes to a sys_winstream
      57              :  *
      58              :  * This function writes the specified number of bytes into the stream.
      59              :  * It will always return synchronously, it does not block or engage in
      60              :  * any kind of synchronization beyond memory write ordering.  Any
      61              :  * bytes passed beyond what can be stored in the buffer will be
      62              :  * silently dropped, but readers can detect their presence via the
      63              :  * sequence number.
      64              :  *
      65              :  * @param ws A sys_winstream to which to write
      66              :  * @param data Pointer to bytes to be written
      67              :  * @param len Number of bytes to write
      68              :  */
      69            1 : void sys_winstream_write(struct sys_winstream *ws,
      70              :                          const char *data, uint32_t len);
      71              : 
      72              : /** @brief Read bytes from a sys_winstream
      73              :  *
      74              :  * This function will read bytes from a sys_winstream into a specified
      75              :  * buffer.  It will always return in constant time, it does not block
      76              :  * or engage in any kind of synchronization beyond memory ordering.
      77              :  * The number of bytes read into the buffer will be returned, but note
      78              :  * that it is possible that an underflow can occur if the writer gets
      79              :  * ahead of our context.  That situation can be detected via the
      80              :  * sequence number returned via a pointer (i.e. if "*seq != old_seq +
      81              :  * return_value", an underflow occurred and bytes were dropped).
      82              :  *
      83              :  * @param ws A sys_winstream from which to read
      84              :  * @param seq A pointer to an integer containing the last sequence
      85              :  *            number read from the stream, or zero to indicate "start
      86              :  *            of stream". It is updated in place and returned for
      87              :  *            future calls and for detecting underflows.
      88              :  * @param buf A buffer into which to store the data read
      89              :  * @param buflen The length of buf in bytes
      90              :  * @return The number of bytes written into the buffer
      91              :  */
      92            1 : uint32_t sys_winstream_read(struct sys_winstream *ws,
      93              :                             uint32_t *seq, char *buf, uint32_t buflen);
      94              : 
      95              : #endif /* ZEPHYR_INCLUDE_SYS_WINSTREAM_H_ */