什麼是 I2S 呢？維基百科詞條這麼講︰

I²S

I²S或I2S（英語：Inter-IC Sound或Integrated Interchip Sound）是IC間傳輸數位音訊資料的一種介面標準，採用序列的方式傳輸2組（左右聲道）資料。I2S常被使用在傳送CD的PCM音訊資料到CD播放器的DAC中。由於I2S將資料訊號和時脈訊號分開傳送，它的抖動（jitter）失真十分地小。

實有來歷的哩︰

History

This standard was introduced in 1986 by Philips (now NXP) and was last revised in 1996.^[1]

Details

The I²S protocol outlines one specific type of PCM digital audio communication with defined parameters outlined in the Philips specification.

The bit clock pulses once for each discrete bit of data on the data lines. The bit clock frequency is the product of the sample rate, the number of bits per channel and the number of channels. So, for example, CD Audio with a sample frequency of 44.1 kHz, with 16 bits of precision and two channels (stereo) has a bit clock frequency of:

44.1 kHz × 16 × 2 = 1.4112 MHz

The word select clock lets the device know whether channel 1 or channel 2 is currently being sent, since I²S allows two channels to be sent on the same data line. For stereo material, the I²S specification states that left audio is transmitted on the low cycle of the word select clock and the right channel is transmitted on the high cycle. The word select clock is a 50% duty-cycle signal that has the same frequency as the sample frequency.

Data are encoded in two’s complement with the MSB (most significant bit) first.^[1]:2

The bus consists of at least three lines:

1. Bit clock line
2. Word clock line – also called word select (WS) or left right clock (LRCLK)
3. At least one multiplexed data line

It may also include the following lines:

1. Master clock (typical 256 x LRCLK)
2. A multiplexed data line for upload

In audio equipment the I²S sometimes forms an external link between the CD transport and a separate DAC box, contrary to purely internal connection within one player box. This may form an alternative to the commonly used AES/EBU or Toslink or S/PDIF standards. There is no standard interconnecting cable for this application. Some manufacturers provide simply three BNC connectors, an 8P8C (“RJ45”) socket or a DE-9 connector. Others like Audio Alchemy (now defunct) used DIN connectors.

樹莓派之 I2S 規格在 BROADCOM

BCM2835

This is the Broadcom chip used in the Raspberry Pi Model A, B, B+, the Compute Module, and the Raspberry Pi Zero.

Please refer to:

• Peripheral specification
• GPU documentation and open source driver
• ARM1176 Processor
• ARM1176JZF-S

Also see the Raspberry Pi 2 Model B’s chip, BCM2836

 

DataSheet 的第一百一拾九頁。

接法及接腳請參照

Introduction to Archphile

 

之說明文件︰

I2S Dacs and the Raspberry Pi

有興趣讀寫驅動程式者，請到這來︰

Linux/sound/soc/bcm/bcm2835-i2s.c

1 /*
2 * ALSA SoC I2S Audio Layer for Broadcom BCM2835 SoC
3 *
4 * Author: Florian Meier <florian.meier@koalo.de>
5 * Copyright 2013
6 *
7 * Based on
8 * Raspberry Pi PCM I2S ALSA Driver
9 * Copyright (c) by Phil Poole 2013
10 *
11 * ALSA SoC I2S (McBSP) Audio Layer for TI DAVINCI processor
12 * Vladimir Barinov, <vbarinov@embeddedalley.com>
13 * Copyright (C) 2007 MontaVista Software, Inc., <source@mvista.com>
14 *
15 * OMAP ALSA SoC DAI driver using McBSP port
16 * Copyright (C) 2008 Nokia Corporation
17 * Contact: Jarkko Nikula <jarkko.nikula@bitmer.com>
18 * Peter Ujfalusi <peter.ujfalusi@ti.com>
19 *
20 * Freescale SSI ALSA SoC Digital Audio Interface (DAI) driver
21 * Author: Timur Tabi <timur@freescale.com>
22 * Copyright 2007-2010 Freescale Semiconductor, Inc.
23 *
24 * This program is free software; you can redistribute it and/or
25 * modify it under the terms of the GNU General Public License
26 * version 2 as published by the Free Software Foundation.
27 *
28 * This program is distributed in the hope that it will be useful, but
29 * WITHOUT ANY WARRANTY; without even the implied warranty of
30 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
31 * General Public License for more details.
32 */
33