1 /*
2 * Copyright (c) 2022 Nordic Semiconductor ASA
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7 #ifndef ZEPHYR_INCLUDE_SYS_SPSC_PBUF_H_
8 #define ZEPHYR_INCLUDE_SYS_SPSC_PBUF_H_
9
10 #include <zephyr/cache.h>
11 #include <zephyr/devicetree.h>
12
13 #ifdef __cplusplus
14 extern "C" {
15 #endif
16
17 /**
18 * @brief Single producer, single consumer packet buffer API
19 * @defgroup spsc_buf SPSC (Single producer, single consumer) packet buffer API
20 * @ingroup datastructure_apis
21 * @{
22 */
23
24 /**@defgroup SPSC_PBUF_FLAGS SPSC packet buffer flags
25 * @{
26 */
27
28 /** @brief Flag indicating that cache shall be handled.
29 *
30 * It shall be used only when packet buffer is shared between two cores as on a single
31 * core cache shall not be handled manually because it results in data corruption.
32 */
33 #define SPSC_PBUF_CACHE BIT(0)
34
35 /** @brief Size of the field which stores maximum utilization. */
36 #define SPSC_PBUF_UTILIZATION_BITS 24
37
38 /** @brief Offset of the field which stores maximum utilization. */
39 #define SPSC_PBUF_UTILIZATION_OFFSET 8
40
41 /**@} */
42
43 #if CONFIG_DCACHE_LINE_SIZE != 0
44 #define Z_SPSC_PBUF_LOCAL_DCACHE_LINE CONFIG_DCACHE_LINE_SIZE
45 #else
46 #define Z_SPSC_PBUF_LOCAL_DCACHE_LINE DT_PROP_OR(CPU, d_cache_line_size, 0)
47 #endif
48
49 #ifndef CONFIG_SPSC_PBUF_REMOTE_DCACHE_LINE
50 #define CONFIG_SPSC_PBUF_REMOTE_DCACHE_LINE 0
51 #endif
52
53 #define Z_SPSC_PBUF_DCACHE_LINE \
54 MAX(CONFIG_SPSC_PBUF_REMOTE_DCACHE_LINE, Z_SPSC_PBUF_LOCAL_DCACHE_LINE)
55
56 /** @brief Maximum packet length. */
57 #define SPSC_PBUF_MAX_LEN 0xFF00
58
59 /** @brief First part of packet buffer control block.
60 *
61 * This part contains only data set during the initialization and data touched
62 * by the reader. If packet is shared between to cores then data changed by
63 * the reader should be on different cache line than the data changed by the
64 * writer.
65 */
66 struct spsc_pbuf_common {
67 uint32_t len; /* Length of data[] in bytes. */
68 uint32_t flags; /* Flags. See @ref SPSC_PBUF_FLAGS */
69 uint32_t rd_idx; /* Index of the first valid byte in data[] */
70 };
71
72 /* Padding to fill cache line. */
73 #define Z_SPSC_PBUF_PADDING \
74 MAX(0, Z_SPSC_PBUF_DCACHE_LINE - (int)sizeof(struct spsc_pbuf_common))
75
76 /** @brief Remaining part of a packet buffer when cache is used.
77 *
78 * It contains data that is only changed by the writer. A gap is added to ensure
79 * that it is in different cache line than the data changed by the reader.
80 */
81 struct spsc_pbuf_ext_cache {
82 uint8_t reserved[Z_SPSC_PBUF_PADDING];
83 uint32_t wr_idx; /* Index of the first free byte in data[] */
84 uint8_t data[]; /* Buffer data. */
85 };
86
87 /** @brief Remaining part of a packet buffer when cache is not used. */
88 struct spsc_pbuf_ext_nocache {
89 uint32_t wr_idx; /* Index of the first free byte in data[] */
90 uint8_t data[]; /* Buffer data. */
91 };
92
93 /**
94 * @brief Single producer, single consumer packet buffer
95 *
96 * The SPSC packet buffer implements lightweight unidirectional packet buffer
97 * with read/write semantics on top of a memory region shared
98 * by the reader and writer. It optionally embeds cache and memory barrier
99 * management to ensure correct data access.
100 *
101 * This structure supports single writer and reader. Data stored in the buffer
102 * is encapsulated to a message (with length header).
103 *
104 */
105 struct spsc_pbuf {
106 struct spsc_pbuf_common common;
107 union {
108 struct spsc_pbuf_ext_cache cache;
109 struct spsc_pbuf_ext_nocache nocache;
110 } ext;
111 };
112
113 /** @brief Get buffer capacity.
114 *
115 * This value is the amount of data that is dedicated for storing packets. Since
116 * each packet is prefixed with 2 byte length header, longest possible packet is
117 * less than that.
118 *
119 * @param pb A buffer.
120 *
121 * @return Packet buffer capacity.
122 */
spsc_pbuf_capacity(struct spsc_pbuf * pb)123 static inline uint32_t spsc_pbuf_capacity(struct spsc_pbuf *pb)
124 {
125 return pb->common.len - sizeof(uint32_t);
126 }
127
128 /**
129 * @brief Initialize the packet buffer.
130 *
131 * This function initializes the packet buffer on top of a dedicated
132 * memory region.
133 *
134 * @param buf Pointer to a memory region on which buffer is
135 * created. When cache is used it must be aligned to
136 * Z_SPSC_PBUF_DCACHE_LINE, otherwise it must
137 * be 32 bit word aligned.
138 * @param blen Length of the buffer. Must be large enough to
139 * contain the internal structure and at least two
140 * bytes of data (one is reserved for written
141 * messages length).
142 * @param flags Option flags. See @ref SPSC_PBUF_FLAGS.
143 * @retval struct spsc_pbuf* Pointer to the created buffer. The pointer
144 * points to the same address as buf.
145 * @retval NULL Invalid buffer alignment.
146 */
147 struct spsc_pbuf *spsc_pbuf_init(void *buf, size_t blen, uint32_t flags);
148
149 /**
150 * @brief Write specified amount of data to the packet buffer.
151 *
152 * It combines @ref spsc_pbuf_alloc and @ref spsc_pbuf_commit into a single call.
153 *
154 * @param pb A buffer to which to write.
155 * @param buf Pointer to the data to be written to the buffer.
156 * @param len Number of bytes to be written to the buffer. Must be positive
157 * but less than @ref SPSC_PBUF_MAX_LEN.
158 * @retval int Number of bytes written, negative error code on fail.
159 * -EINVAL, if len == 0.
160 * -ENOMEM, if len is bigger than the buffer can fit.
161 */
162 int spsc_pbuf_write(struct spsc_pbuf *pb, const char *buf, uint16_t len);
163
164 /**
165 * @brief Allocate space in the packet buffer.
166 *
167 * This function attempts to allocate @p len bytes of continuous memory within
168 * the packet buffer. An internal padding is added at the end of the buffer, if
169 * wrapping occurred during allocation. Apart from padding, allocation does not
170 * change the state of the buffer so if after allocation packet is not needed
171 * a commit is not needed.
172 *
173 * Allocated buffer must be committed (@ref spsc_pbuf_commit) to make the packet
174 * available for reading.
175 *
176 * Packet buffer ensures that allocated buffers are 32 bit word aligned.
177 *
178 * @note If data cache is used, it is the user responsibility to write back the
179 * new data.
180 *
181 * @param[in] pb A buffer to which to write.
182 * @param[in] len Allocation length. Must be positive. If less than @ref SPSC_PBUF_MAX_LEN
183 * then if requested length cannot be allocated, an attempt to allocate
184 * largest possible is performed (which may include adding wrap padding).
185 * If @ref SPSC_PBUF_MAX_LEN is used then an attempt to allocate largest
186 * buffer without applying wrap padding is performed.
187 * @param[out] buf Location where buffer address is written on successful allocation.
188 *
189 * @retval non-negative Amount of space that got allocated. Can be equal or smaller than %p len.
190 * @retval -EINVAL if @p len is forbidden.
191 */
192 int spsc_pbuf_alloc(struct spsc_pbuf *pb, uint16_t len, char **buf);
193
194 /**
195 * @brief Commit packet to the buffer.
196 *
197 * Commit a packet which was previously allocated (@ref spsc_pbuf_alloc).
198 * If cache is used, cache writeback is performed on the written data.
199 *
200 * @param pb A buffer to which to write.
201 * @param len Packet length. Must be equal or less than the length used for allocation.
202 */
203 void spsc_pbuf_commit(struct spsc_pbuf *pb, uint16_t len);
204
205 /**
206 * @brief Read specified amount of data from the packet buffer.
207 *
208 * Single read allows to read the message send by the single write.
209 * The provided %p buf must be big enough to store the whole message.
210 *
211 * It combines @ref spsc_pbuf_claim and @ref spsc_pbuf_free into a single call.
212 *
213 * @param pb A buffer from which data will be read.
214 * @param buf Data pointer to which read data will be written.
215 * If NULL, len of stored message is returned.
216 * @param len Number of bytes to be read from the buffer.
217 * @retval int Bytes read, negative error code on fail.
218 * Bytes to be read, if buf == NULL.
219 * -ENOMEM, if message can not fit in provided buf.
220 * -EAGAIN, if not whole message is ready yet.
221 */
222 int spsc_pbuf_read(struct spsc_pbuf *pb, char *buf, uint16_t len);
223
224 /**
225 * @brief Claim packet from the buffer.
226 *
227 * It claims a single packet from the buffer in the order of the commitment
228 * by the @ref spsc_pbuf_commit function. The first committed packet will be claimed first.
229 * The returned buffer is 32 bit word aligned and points to the continuous memory.
230 * Claimed packet must be freed using the @ref spsc_pbuf_free function.
231 *
232 * @note If data cache is used, cache is invalidate on the packet.
233 *
234 * @param[in] pb A buffer from which packet will be claimed.
235 * @param[in,out] buf A location where claimed packet address is written.
236 * It is 32 bit word aligned and points to the continuous memory.
237 *
238 * @retval 0 No packets in the buffer.
239 * @retval positive packet length.
240 */
241 uint16_t spsc_pbuf_claim(struct spsc_pbuf *pb, char **buf);
242
243 /**
244 * @brief Free the packet to the buffer.
245 *
246 * Packet must be claimed (@ref spsc_pbuf_claim) before it can be freed.
247 *
248 * @param pb A packet buffer from which packet was claimed.
249 * @param len Claimed packet length.
250 */
251 void spsc_pbuf_free(struct spsc_pbuf *pb, uint16_t len);
252
253 /**
254 * @brief Get maximum utilization of the packet buffer.
255 *
256 * Function can be used to tune the buffer size. Feature is enabled by
257 * CONFIG_SPSC_PBUF_UTILIZATION. Utilization is updated by the consumer.
258 *
259 * @param pb A packet buffer.
260 *
261 * @retval -ENOTSUP Feature not enabled.
262 * @retval non-negative Maximum utilization.
263 */
264 int spsc_pbuf_get_utilization(struct spsc_pbuf *pb);
265 /**
266 * @}
267 */
268
269 #ifdef __cplusplus
270 }
271 #endif
272
273 #endif /* ZEPHYR_INCLUDE_SYS_SPSC_PBUF_H_ */
274
