流模塊單獨(dú)分出來講是因?yàn)閮?nèi)容相對比較多船逮，而且也有一定難度。流模塊可以對應(yīng)數(shù)據(jù)的生產(chǎn)者/消費(fèi)者模型状勤，生產(chǎn)者可以向流里寫數(shù)據(jù)（生產(chǎn)數(shù)據(jù)）鞋怀，消費(fèi)者從流里讀取數(shù)據(jù)（消費(fèi)數(shù)據(jù)）。并且持搜，通過回調(diào)接口密似，可以實(shí)現(xiàn)自動(dòng)流控。VSF中的流模塊的實(shí)現(xiàn)葫盼，也可以用來闡述面向?qū)ο蟮木幊趟枷胄劣眩驗(yàn)榱髦皇且粋€(gè)抽象類，實(shí)際使用的是具體的fifo流剪返、buffer流或者multibuf流等具體內(nèi)存結(jié)構(gòu)實(shí)現(xiàn)的流。所以邓梅，流只是一個(gè)標(biāo)準(zhǔn)接口脱盲，如果一個(gè)模塊支持流接口的話，就可以很方便的和其他支持流接口的模塊對接日缨。比如钱反，wave播放模塊的輸入流，可以接到文件流匣距，對應(yīng)播放本地的wav文件面哥；也可以接到http流，對用播放網(wǎng)上的wav文件毅待，而wave播放模塊并不需要在意流的來源尚卫。
下面介紹一下流的接口，和實(shí)現(xiàn)自動(dòng)流控的原理：
struct vsf_stream_cb_t
{
void *param;
void (*on_inout)(void *param);
void (*on_connect)(void *param);
void (*on_disconnect)(void *param);
};
struct vsf_stream_t
{
// user_mem points to user structure, eg queue/fifo
struct vsf_stream_op_t const *op;
// callback_tx is notification for tx end of the stream
// when rx end read the data out, will notify the tx end
struct vsf_stream_cb_t callback_tx;
// callback_rx is notification for rx end of the stream
// when tx end write the data in, will notify the rx end
struct vsf_stream_cb_t callback_rx;
bool tx_ready;
bool rx_ready;
bool overflow;
};
vsf_err_t stream_init(struct vsf_stream_t *stream);
vsf_err_t stream_fini(struct vsf_stream_t *stream);
uint32_t stream_write(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer);
uint32_t stream_read(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer);
uint32_t stream_get_data_size(struct vsf_stream_t *stream);
uint32_t stream_get_free_size(struct vsf_stream_t *stream);
uint32_t stream_get_wbuf(struct vsf_stream_t *stream, uint8_t **ptr);
uint32_t stream_get_rbuf(struct vsf_stream_t *stream, uint8_t **ptr);
void stream_connect_rx(struct vsf_stream_t *stream);
void stream_connect_tx(struct vsf_stream_t *stream);
void stream_disconnect_rx(struct vsf_stream_t *stream);
void stream_disconnect_tx(struct vsf_stream_t *stream);
上面是流的數(shù)據(jù)結(jié)構(gòu)尸红，和操作接口吱涉。初始化和讀寫函數(shù)一看就能明白，stream_get_data_size是得到流里的數(shù)據(jù)大小外里，stream_get_free_size是得到流里的空余空間大小怎爵。stream_get_wbuf和stream_get_rbuf用于得到當(dāng)前的讀寫指針，只在非常特殊的情況下使用盅蝗。stream_connect_XX和stream_disconnect_XX是流的接收或者發(fā)送端的連接或者斷開鳖链。vsf_stream_t中，callback_XX是接收或者發(fā)送端設(shè)置的回調(diào)函數(shù)墩莫，當(dāng)流的一端連接/斷開/讀寫數(shù)據(jù)的時(shí)候芙委，通過回調(diào)接口通知流的另一端。
基于callback狂秦，就可以實(shí)現(xiàn)流控题山，生產(chǎn)者寫入數(shù)據(jù)到流的時(shí)候，會(huì)通知消費(fèi)者去消費(fèi)數(shù)據(jù)故痊；消費(fèi)者消費(fèi)了數(shù)據(jù)的時(shí)候顶瞳，也會(huì)通知生產(chǎn)者。生產(chǎn)者可以通過stream_get_free_size來得到流里空余空間的小大，只有大于生產(chǎn)者一次可產(chǎn)生的數(shù)據(jù)的時(shí)候（比如對于全速USB慨菱，就是64字節(jié)的最大ep大醒媛纭），生產(chǎn)者才會(huì)產(chǎn)生數(shù)據(jù)符喝。如果空余空間不夠的話闪彼，生產(chǎn)者只需要等待消費(fèi)者消費(fèi)數(shù)據(jù)后，再次通知生產(chǎn)者协饲，然后生產(chǎn)者再判斷是否有足夠的空余空間畏腕。當(dāng)然，實(shí)現(xiàn)流控的前提是生產(chǎn)者可以控制數(shù)據(jù)的產(chǎn)生茉稠。
流的實(shí)現(xiàn)：
uint32_t stream_read(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer)
{
uint32_t count = stream->op->read(stream, buffer);
if (stream->tx_ready && (stream->callback_tx.on_inout != NULL) && count)
{
stream->callback_tx.on_inout(stream->callback_tx.param);
}
return count;
}
uint32_t stream_write(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer)
{
uint32_t count = stream->op->write(stream, buffer);
if (count < buffer->size)
{
stream->overflow = true;
}
if (stream->rx_ready && (stream->callback_rx.on_inout != NULL) && count)
{
stream->callback_rx.on_inout(stream->callback_rx.param);
}
return count;
}
這里只是簡單用讀寫接口舉例描馅，實(shí)際的讀寫操作，有op參數(shù)里指定的讀寫接口實(shí)現(xiàn)而线。代碼里铭污，也只是簡單調(diào)用op指定的讀寫接口，然后判斷是否溢出以及是否需要調(diào)用回調(diào)接口膀篮。
流結(jié)構(gòu)中嘹狞，并沒有指定緩沖的數(shù)據(jù)結(jié)構(gòu)，因?yàn)閼?yīng)用可以根據(jù)實(shí)際應(yīng)用需求誓竿，來選擇緩沖類型磅网。這里用最常用的fifo流來舉例：
struct vsf_fifostream_t
{
struct vsf_stream_t stream;
struct vsf_fifo_t mem;
};
static void fifo_stream_init(struct vsf_stream_t *stream)
{
struct vsf_fifostream_t *fifostream = (struct vsf_fifostream_t *)stream;
vsf_fifo_init(&fifostream->mem);
}
static uint32_t fifo_stream_get_data_length(struct vsf_stream_t *stream)
{
struct vsf_fifostream_t *fifostream = (struct vsf_fifostream_t *)stream;
return vsf_fifo_get_data_length(&fifostream->mem);
}
static uint32_t
fifo_stream_write(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer)
{
struct vsf_fifostream_t *fifostream = (struct vsf_fifostream_t *)stream;
return vsf_fifo_push(&fifostream->mem, buffer->size, buffer->buffer);
}
static uint32_t
fifo_stream_read(struct vsf_stream_t *stream, struct vsf_buffer_t *buffer)
{
struct vsf_fifostream_t *fifostream = (struct vsf_fifostream_t *)stream;
return vsf_fifo_pop(&fifostream->mem, buffer->size, buffer->buffer);
}
const struct vsf_stream_op_t fifostream_op =
{
.init = fifo_stream_init,
.fini = fifo_stream_init,
.write = fifo_stream_write,
.read = fifo_stream_read,
.get_data_length = fifo_stream_get_data_length,
.get_avail_length = fifo_stream_get_avail_length,
.get_wbuf = fifo_stream_get_wbuf,
.get_rbuf = fifo_stream_get_rbuf,
};
這里只是列舉了幾個(gè)函數(shù)。fifo流繼承自vsf_stream_t筷屡，并且指定了fifo的緩沖類型知市。fifostream_op里指定了fifo流的各種操作接口，實(shí)際實(shí)現(xiàn)只是簡單調(diào)用fifo模塊的對應(yīng)接口速蕊∩┍可以把vsf_fifostream_t強(qiáng)制類型轉(zhuǎn)換為vsf_stream_t梧却，就可以使用標(biāo)準(zhǔn)的流接口了遏插。實(shí)際可以通過宏來實(shí)現(xiàn)各種不同類型的流的強(qiáng)制轉(zhuǎn)換：
#define STREAM_INIT(s) stream_init((struct vsf_stream_t *)(s))
#define STREAM_FINI(s) stream_fini((struct vsf_stream_t *)(s))
#define STREAM_WRITE(s, b) stream_write((struct vsf_stream_t *)(s), (b))
#define STREAM_READ(s, b) stream_read((struct vsf_stream_t *)(s), (b))
#define STREAM_GET_DATA_SIZE(s) stream_get_data_size((struct vsf_stream_t *)(s))
#define STREAM_GET_FREE_SIZE(s) stream_get_free_size((struct vsf_stream_t *)(s))
#define STREAM_GET_WBUF(s, p) stream_get_wbuf((struct vsf_stream_t *)(s), (p))
#define STREAM_GET_RBUF(s, p) stream_get_rbuf((struct vsf_stream_t *)(s), (p))
#define STREAM_CONNECT_RX(s) stream_connect_rx((struct vsf_stream_t *)(s))
#define STREAM_CONNECT_TX(s) stream_connect_tx((struct vsf_stream_t *)(s))
#define STREAM_DISCONNECT_RX(s) stream_disconnect_rx((struct vsf_stream_t *)(s))
#define STREAM_DISCONNECT_TX(s) stream_disconnect_tx((struct vsf_stream_t *)(s))
和標(biāo)準(zhǔn)接口只是大小寫的區(qū)別渗柿。
