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/* SPDX-License-Identifier: GPL-2.0-or-later */
* Helper functions for indirect PCM data transfer to a simple FIFO in
* hardware (small, no possibility to read "hardware io position",
* updating position done by interrupt, ...)
* Copyright (c) by 2007 Joachim Foerster <>
* Based on "pcm-indirect.h" (alsa-driver-1.0.13) by
* Copyright (c) by Takashi Iwai <>
* Jaroslav Kysela <>
/* struct snd_pcm_substream, struct snd_pcm_runtime, snd_pcm_uframes_t */
#include <sound/pcm.h>
/* Debug options for code which may be removed completely in a final version */
#define SND_PCM_INDIRECT2_STAT /* turn on some "statistics" about the
* process of copying bytes from the
* intermediate buffer to the hardware
* fifo and the other way round
struct snd_pcm_indirect2 {
unsigned int hw_buffer_size; /* Byte size of hardware buffer */
int hw_ready; /* playback: 1 = hw fifo has room left,
* 0 = hw fifo is full
unsigned int min_multiple;
int min_periods; /* counts number of min. periods until
* min_multiple is reached
int min_period_count; /* counts bytes to count number of
* min. periods
unsigned int sw_buffer_size; /* Byte size of software buffer */
/* sw_data: position in intermediate buffer, where we will read (or
* write) from/to next time (to transfer data to/from HW)
unsigned int sw_data; /* Offset to next dst (or src) in sw
* ring buffer
/* easiest case (playback):
* sw_data is nearly the same as ~ runtime->control->appl_ptr, with the
* exception that sw_data is "behind" by the number if bytes ALSA wrote
* to the intermediate buffer last time.
* A call to ack() callback synchronizes both indirectly.
/* We have no real sw_io pointer here. Usually sw_io is pointing to the
* current playback/capture position _inside_ the hardware. Devices
* with plain FIFOs often have no possibility to publish this position.
* So we say: if sw_data is updated, that means bytes were copied to
* the hardware, we increase sw_io by that amount, because there have
* to be as much bytes which were played. So sw_io will stay behind
* sw_data all the time and has to converge to sw_data at the end of
* playback.
unsigned int sw_io; /* Current software pointer in bytes */
/* sw_ready: number of bytes ALSA copied to the intermediate buffer, so
* it represents the number of bytes which wait for transfer to the HW
int sw_ready; /* Bytes ready to be transferred to/from hw */
/* appl_ptr: last known position of ALSA (where ALSA is going to write
* next time into the intermediate buffer
snd_pcm_uframes_t appl_ptr; /* Last seen appl_ptr */
unsigned int bytes2hw;
int check_alignment;
unsigned int zeros2hw;
unsigned int mul_elapsed;
unsigned int mul_elapsed_real;
unsigned long firstbytetime;
unsigned long lastbytetime;
unsigned long firstzerotime;
unsigned int byte_sizes[64];
unsigned int zero_sizes[64];
unsigned int min_adds[8];
unsigned int mul_adds[8];
unsigned int zero_times[3750]; /* = 15s */
unsigned int zero_times_saved;
unsigned int zero_times_notsaved;
unsigned int irq_occured;
unsigned int pointer_calls;
unsigned int lastdifftime;
typedef size_t (*snd_pcm_indirect2_copy_t) (struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec,
size_t bytes);
typedef size_t (*snd_pcm_indirect2_zero_t) (struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec);
void snd_pcm_indirect2_stat(struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec);
snd_pcm_indirect2_pointer(struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec);
snd_pcm_indirect2_playback_interrupt(struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec,
snd_pcm_indirect2_copy_t copy,
snd_pcm_indirect2_zero_t zero);
snd_pcm_indirect2_capture_interrupt(struct snd_pcm_substream *substream,
struct snd_pcm_indirect2 *rec,
snd_pcm_indirect2_copy_t copy,
snd_pcm_indirect2_zero_t null);
#endif /* __SOUND_PCM_INDIRECT2_H */