pcm1865的i2s协议2单通道已经实现，pcm格式的4单通道怎么实现？

关于I2S和PCM：

I2S is a common 4 wire DAI used in HiFi, STB and portable devices. The Tx and
Rx lines are used for audio transmission, whilst the bit clock (BCLK) and
left/right clock (LRC) synchronise the link. I2S is flexible in that either the
controller or CODEC can drive (master) the BCLK and LRC clock lines. Bit clock
usually varies depending on the sample rate and the master system clock
(SYSCLK). LRCLK is the same as the sample rate. A few devices support separate
ADC and DAC LRCLKs, this allows for simultaneous capture and playback at
different sample rates.

I2S has several different operating modes:-

 I2S - MSB is transmitted on the falling edge of the first BCLK after LRC
         transition.

 Left Justified - MSB is transmitted on transition of LRC.

 Right Justified - MSB is transmitted sample size BCLKs before LRC
                     transition.

PCM
===

PCM is another 4 wire interface, very similar to I2S, which can support a more
flexible protocol. It has bit clock (BCLK) and sync (SYNC) lines that are used
to synchronise the link whilst the Tx and Rx lines are used to transmit and
receive the audio data. Bit clock usually varies depending on sample rate
whilst sync runs at the sample rate. PCM also supports Time Division
Multiplexing (TDM) in that several devices can use the bus simultaneously (this
is sometimes referred to as network mode).

Common PCM operating modes:-

Mode A - MSB is transmitted on falling edge of first BCLK after FRAME/SYNC.

 Mode B - MSB is transmitted on rising edge of FRAME/SYNC.