一、实验环境
1.1 虚拟机环境
a) Vmware版本:Vmware Workstation 12.5.7
b) Ubuntu版本:9.10
c) 内核版本:2.6.31.14
d) toolchain版本:arm-linux-gcc 4.3.2
1.2 开发板
优龙FS2410开发板,UDA1341声卡
内核版本:3.4.2
二、声卡数据传输的原理(以播放为例)
(1) 驱动程序分配一个buffer:s2c2440_dma_new
(2) app不断写一个个period数据到buffer(appl_ptr以frame为单位) 。一个period包含多个frame,一个frame就是一个采样数据
(3) 驱动不断从buffer里取出一个period:load_dma_period,启动DMA传输:s3c2440_dma_start,发送给声卡
(4)传输完毕,产生中断):s3c2440_dma2_irq ,更新状态(hw_ptr,以frame为单位)
三、具体实现(s3c2440_dma.c)
注:内核中关于s3c24xx的DMA操作的代码框架非常复杂,暂时未仔细研究(可参考:李兰溪 S3C24XX DMA框架源码分析)。而我们自制的驱动,则简化了很多,但基本思想和流程是和内核一致的。
准备工作
1. 定义好DMA操作相关的寄存器,并进行ioremap,以便后续的访问
#define DMA0_BASE_ADDR 0x4B000000
#define DMA1_BASE_ADDR 0x4B000040
#define DMA2_BASE_ADDR 0x4B000080
#define DMA3_BASE_ADDR 0x4B0000C0
struct s3c_dma_regs {
unsigned long disrc;
unsigned long disrcc;
unsigned long didst;
unsigned long didstc;
unsigned long dcon;
unsigned long dstat;
unsigned long dcsrc;
unsigned long dcdst;
unsigned long dmasktrig;
};
static volatile struct s3c_dma_regs *dma_regs;
static int s3c2440_dma_init(void)
{
dma_regs = ioremap(DMA2_BASE_ADDR, sizeof(struct s3c_dma_regs));
platform_device_register(&s3c2440_dma_dev);
platform_driver_register(&s3c2440_dma_drv);
return 0;
}
static void s3c2440_dma_exit(void)
{
platform_device_unregister(&s3c2440_dma_dev);
platform_driver_unregister(&s3c2440_dma_drv);
iounmap(dma_regs);
}
2. 实现几个基础函数,供后续s3c2440_dma_prepare、s3c2440_dma2_irq和s3c2440_dma_trigger调用
/* 数据传输: 源,目的,长度 */
static void load_dma_period(void)
{
/* 把源,目的,长度告诉DMA */
dma_regs->disrc = playback_dma_info.phy_addr + playback_dma_info.dma_ofs; /* 源的物理地址 */
dma_regs->disrcc = (0<<1) | (0<<0); /* 源位于AHB总线, 源地址递增 */
dma_regs->didst = 0x55000010; /* 目的的物理地址 IIS fifo entry*/
dma_regs->didstc = (0<<2) | (1<<1) | (1<<0); /* 目的位于APB总线, 目的地址不变 */
/*
handshake mode
DACK and DREQ are synchronized to PCLK
Enable/Disable the interrupt setting for CURR_TC
A unit transfer
single service mode
select I2SSDO of DCON2 as DMA request source
hardware trigger DMA request
datasize to be transfered: half word
2(bytes)*1(unit)*initial transfer_count = len
==>transfer_count=len/2
*/
/* bit22: 1-noreload */
//传输的长度(datasize是half word即2个字节):playback_dma_info.period_size/2
dma_regs->dcon = (1<<31)|(0<<30)|(1<<29)|(0<<28)|(0<<27)|(0<<24)|(1<<23)|(1<<22)|(1<<20)|(playback_dma_info.period_size/2);
/* 使能中断,单个传输,硬件触发 */
}
static void s3c2440_dma_start(void)
{
/* 启动DMA */
dma_regs->dmasktrig = (1<<1);
}
static void s3c2440_dma_stop(void)
{
/* 停止DMA */
dma_regs->dmasktrig &= ~(1<<1);
}
3.1 实现s3c2440_dma_platform.pcm_new(即s3c2440_dma_new)
(参考 soundsocsamsungdma.c 的 dma_new)
static int s3c2440_dma_new(struct snd_soc_pcm_runtime *rtd)
{
struct snd_card *card = rtd->card->snd_card;
struct snd_pcm *pcm = rtd->pcm;
struct snd_pcm_substream *substream = pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream;
struct snd_dma_buffer *buf = &substream->dma_buffer;
/*
snd_dma_buffer的作用:
在hw_params阶段,snd_soc_platform_driver的ops->hw_params会被调用,通常会使用snd_pcm_set_runtime_buffer()
把substream->dma_buffer的值拷贝到substream->runtime的相关字段中(.dma_area, .dma_addr, .dma_bytes),
这样以后就可以通过substream->runtime获得这些地址和大小信息了。因为有播放和录音两个substream,而runtime始终指向当前使用的substream,
所以便于跟踪substream。
*/
int ret = 0;
/* 1. 分配DMA BUFFER */
if (!card->dev->dma_mask) //这段代码,是后来调试时发现,必须要加的
card->dev->dma_mask = &dma_mask;
if (!card->dev->coherent_dma_mask)
card->dev->coherent_dma_mask = DMA_BIT_MASK(32);
if (pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream) {
playback_dma_info.virt_addr = (unsigned int)dma_alloc_writecombine(pcm->card->dev, s3c2440_dma_hardware.buffer_bytes_max,
&playback_dma_info.phy_addr, GFP_KERNEL);
if (!playback_dma_info.virt_addr)
{
return -ENOMEM;
}
playback_dma_info.buf_max_size = s3c2440_dma_hardware.buffer_bytes_max;
buf->dev.type = SNDRV_DMA_TYPE_DEV;
buf->dev.dev = pcm->card->dev;
buf->private_data = NULL;
buf->area = (unsigned char *)playback_dma_info.virt_addr; //这句话是后来调试时,才发现需要加的
buf->bytes = playback_dma_info.buf_max_size;
buf->addr = playback_dma_info.phy_addr;
}
return ret;
//为了简化,先去掉录音功能
}
3.2 实现s3c2440_dma_platform.ops.open(即s3c2440_dma_open)
(参考 soundsocsamsungdma.c 的 dma_open)
static const struct snd_pcm_hardware s3c2440_dma_hardware = {
.info = SNDRV_PCM_INFO_INTERLEAVED |
SNDRV_PCM_INFO_BLOCK_TRANSFER |
SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_MMAP_VALID |
SNDRV_PCM_INFO_PAUSE |
SNDRV_PCM_INFO_RESUME,
.formats = SNDRV_PCM_FMTBIT_S16_LE |
SNDRV_PCM_FMTBIT_U16_LE |
SNDRV_PCM_FMTBIT_U8 |
SNDRV_PCM_FMTBIT_S8,
.channels_min = 2,
.channels_max = 2,
.buffer_bytes_max = 128*1024, //在s3c2440_dma_new里被用于指定dma_alloc_writecombine的size参数
.period_bytes_min = PAGE_SIZE,
.period_bytes_max = PAGE_SIZE*2,
.periods_min = 2,
.periods_max = 128,
.fifo_size = 32,
};
//目前只支持播放
static int s3c2440_dma_open(struct snd_pcm_substream *substream)
{
struct snd_pcm_runtime *runtime = substream->runtime;
int ret;
/* 设置属性 */
snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS); //约束:periods必须是整数
snd_soc_set_runtime_hwparams(substream, &s3c2440_dma_hardware);
/*
snd_soc_set_runtime_hwparams的作用: 把s3c2440_dma_hardware的各个属性赋给substream->runtime->hw,
后续在snd_pcm_open_file==>snd_pcm_open_substream==>snd_pcm_hw_constraints_complete==>
snd_pcm_hw_constraint_minmax里会调用诸如snd_pcm_hw_constraint_minmax(runtime,
SNDRV_PCM_HW_PARAM_CHANNELS, hw->channels_min, hw->channels_max);
*/
/* 注册中断 */
ret = request_irq(IRQ_DMA2, s3c2440_dma2_irq, IRQF_DISABLED, "myalsa for playback", substream);
if (ret)
{
printk("request_irq error!n");
return -EIO;
}
return 0;
}
static int s3c2440_dma_close(struct snd_pcm_substream *substream)
{
free_irq(IRQ_DMA2, substream);
return 0;
}
3.3 实现s3c2440_dma_platform.ops. hw_params(即s3c2440_dma_hw_params)
(参考 soundsocsamsungdma.c 的 dma_hw_params)
static int s3c2440_dma_hw_params(struct snd_pcm_substream *substream, struct snd_pcm_hw_params *params)
{
struct snd_pcm_runtime *runtime = substream->runtime;
unsigned long totbytes = params_buffer_bytes(params);
/* 根据params设置DMA */
/* 关于snd_pcm_set_runtime_buffer的作用,可看上文s3c2440_dma_new 关于snd_dma_buffer的注释*/
snd_pcm_set_runtime_buffer(substream, &substream->dma_buffer);
/*
s3c2440_dma_new分配了很大的DMA BUFFER,而dma_bytes表明app决定使用多大
runtime->dma_bytes被snd_pcm_lib_readv_transfer和snd_pcm_lib_writev_transfer用来和App之间传输数据
*/
runtime->dma_bytes = totbytes;
playback_dma_info.buffer_size = totbytes;
playback_dma_info.period_size = params_period_bytes(params); //记录了app在每个period里传输的数据大小(单位:byte),一个period里包含多个frame
return 0;
}
3.4 实现s3c2440_dma_prepare
(参考 soundsocsamsungdma.c 的 dma_prepare)
static int s3c2440_dma_prepare(struct snd_pcm_substream *substream)
{
/* 准备DMA传输 */
/* 复位各种状态信息 */
playback_dma_info.dma_ofs = 0;
playback_dma_info.be_running = 0;
/* 加载第1个period */
load_dma_period(); //仿照裸板程序的dma_init()
return 0;
}
3.5 实现s3c2440_dma_trigger
(参考 soundsocsamsungdma.c 的 dma_trigger)
static int s3c2440_dma_trigger(struct snd_pcm_substream *substream, int cmd)
{
int ret = 0;
/* 根据cmd启动或停止DMA传输 */
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
case SNDRV_PCM_TRIGGER_RESUME:
case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
/* 启动DMA传输 */
playback_dma_info.be_running = 1;
s3c2440_dma_start();
break;
case SNDRV_PCM_TRIGGER_STOP:
case SNDRV_PCM_TRIGGER_SUSPEND:
case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
/* 停止DMA传输 */
playback_dma_info.be_running = 0;
s3c2440_dma_stop();
break;
default:
ret = -EINVAL;
break;
}
return ret;
}
3.6 实现s3c2440_dma2_irq
(参考 soundsocsamsungdma.c 的 audio_buffdone)
static irqreturn_t s3c2440_dma2_irq(int irq, void *devid)
{
struct snd_pcm_substream *substream = devid;
/* 更新状态信息 */
playback_dma_info.dma_ofs += playback_dma_info.period_size;
if (playback_dma_info.dma_ofs >= playback_dma_info.buffer_size) // buffer_size来自于params_buffer_bytes(params),即App需要使用的缓冲区大小
playback_dma_info.dma_ofs = 0; //如果当前DMA缓冲区中已传输的位置,超出了playback_dma_info.buffer_size,那么回零
/* 更新hw_ptr等信息,
* 并且判断:如果buffer里没有数据了,则调用trigger来停止DMA
*/
snd_pcm_period_elapsed(substream);
/*
snd_pcm_period_elapsed为了查询当前已传输的DMA数据在ring_buffer中的位置,会调用snd_pcm_update_hw_ptr0==>substream->ops->pointer(即soc_pcm_pointer) ==>