diff options
Diffstat (limited to 'Documentation/DocBook/writing-an-alsa-driver.tmpl')
| -rw-r--r-- | Documentation/DocBook/writing-an-alsa-driver.tmpl | 58 |
1 files changed, 29 insertions, 29 deletions
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl index fb32aead5a0b..bd6fee22c4dd 100644 --- a/Documentation/DocBook/writing-an-alsa-driver.tmpl +++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl @@ -871,9 +871,8 @@ <para> This function itself doesn't allocate the data space. The data must be allocated manually beforehand, and its pointer is passed - as the argument. This pointer is used as the - (<parameter>chip</parameter> identifier in the above example) - for the instance. + as the argument. This pointer (<parameter>chip</parameter> in the + above example) is used as the identifier for the instance. </para> <para> @@ -2304,7 +2303,7 @@ struct _snd_pcm_runtime { <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you have to specify whether the mmap is supported and which interleaved format is supported. - When the is supported, add the + When the hardware supports mmap, add the <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the hardware supports the interleaved or the non-interleaved formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or @@ -2898,7 +2897,7 @@ struct _snd_pcm_runtime { <para> When the pcm supports the pause operation (given in the info - field of the hardware table), the <constant>PAUSE_PUSE</constant> + field of the hardware table), the <constant>PAUSE_PUSH</constant> and <constant>PAUSE_RELEASE</constant> commands must be handled here, too. The former is the command to pause the pcm, and the latter to restart the pcm again. @@ -3085,7 +3084,7 @@ struct _snd_pcm_runtime { <section id="pcm-interface-interrupt-handler-timer"> <title>High frequency timer interrupts</title> <para> - This happense when the hardware doesn't generate interrupts + This happens when the hardware doesn't generate interrupts at the period boundary but issues timer interrupts at a fixed timer rate (e.g. es1968 or ymfpci drivers). In this case, you need to check the current hardware @@ -3251,18 +3250,19 @@ struct _snd_pcm_runtime { <title>Example of Hardware Constraints for Channels</title> <programlisting> <![CDATA[ - static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, + static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule) { struct snd_interval *c = hw_param_interval(params, - SNDRV_PCM_HW_PARAM_CHANNELS); + SNDRV_PCM_HW_PARAM_CHANNELS); struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); - struct snd_mask fmt; + struct snd_interval ch; - snd_mask_any(&fmt); /* Init the struct */ - if (c->min < 2) { - fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; - return snd_mask_refine(f, &fmt); + snd_interval_any(&ch); + if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { + ch.min = ch.max = 1; + ch.integer = 1; + return snd_interval_refine(c, &ch); } return 0; } @@ -3278,35 +3278,35 @@ struct _snd_pcm_runtime { <programlisting> <![CDATA[ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, - hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT, - -1); + hw_rule_channels_by_format, NULL, + SNDRV_PCM_HW_PARAM_FORMAT, -1); ]]> </programlisting> </informalexample> </para> <para> - The rule function is called when an application sets the number of - channels. But an application can set the format before the number of - channels. Thus you also need to define the inverse rule: + The rule function is called when an application sets the PCM + format, and it refines the number of channels accordingly. + But an application may set the number of channels before + setting the format. Thus you also need to define the inverse rule: <example> - <title>Example of Hardware Constraints for Channels</title> + <title>Example of Hardware Constraints for Formats</title> <programlisting> <![CDATA[ - static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, + static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, struct snd_pcm_hw_rule *rule) { struct snd_interval *c = hw_param_interval(params, - SNDRV_PCM_HW_PARAM_CHANNELS); + SNDRV_PCM_HW_PARAM_CHANNELS); struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); - struct snd_interval ch; + struct snd_mask fmt; - snd_interval_any(&ch); - if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { - ch.min = ch.max = 1; - ch.integer = 1; - return snd_interval_refine(c, &ch); + snd_mask_any(&fmt); /* Init the struct */ + if (c->min < 2) { + fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; + return snd_mask_refine(f, &fmt); } return 0; } @@ -3321,8 +3321,8 @@ struct _snd_pcm_runtime { <programlisting> <![CDATA[ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, - hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS, - -1); + hw_rule_format_by_channels, NULL, + SNDRV_PCM_HW_PARAM_CHANNELS, -1); ]]> </programlisting> </informalexample> |
