1 /*
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2025 Goran Mekić
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #include <sys/soundcard.h>
29
30 #include <err.h>
31 #include <fcntl.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <unistd.h>
36
37 /*
38 * Minimal configuration for OSS. For real world applications, this structure
39 * will probably contain many more fields
40 */
41 struct config {
42 char *device;
43 int mode;
44 int fd;
45 int format;
46 int sample_count;
47 int sample_rate;
48 int sample_size;
49 int chsamples;
50 int mmap;
51 void *buf;
52 oss_audioinfo audio_info;
53 audio_buf_info buffer_info;
54 };
55
56 /*
57 * The buffer size used by OSS is (2 ^ exponent) * number_of_fragments.
58 * Exponent values range between 4 and 16, so this function looks for the
59 * smallest exponent which can fit a buffer of size "x". The fragments
60 * determine in how many chunks the buffer will be sliced into, hence if the
61 * exponent is 4, and number of fragments is 2, the requested size will be 2^4
62 * * 2 = 32. Please note that the buffer size is in bytes, not samples. For
63 * example, a 24-bit sample will be represented with 3 bytes. If you're porting
64 * an audio application from Linux, you should be aware that 24-bit samples on
65 * it are represented with 4 bytes (usually int). The idea of a total buffer
66 * size that holds number of fragments is to allow application to be
67 * number_of_fragments - 1 late. That's called jitter tolerance.
68 *
69 * Official OSS development howto:
70 * http://manuals.opensound.com/developer/DSP.html
71 */
72 static inline int
size2exp(int x)73 size2exp(int x)
74 {
75 int exp = 0;
76
77 while ((1 << exp) < x)
78 exp++;
79
80 return (exp);
81 }
82
83 static void
oss_init(struct config * config)84 oss_init(struct config *config)
85 {
86 unsigned long request = SNDCTL_DSP_GETOSPACE;
87 int tmp = 0;
88
89 if ((config->fd = open(config->device, config->mode)) < 0)
90 err(1, "Error opening the device %s", config->device);
91
92 /* Get device information */
93 if (ioctl(config->fd, SNDCTL_ENGINEINFO, &config->audio_info) < 0)
94 err(1, "Unable to get device info");
95
96 /* Get device capabilities */
97 if (ioctl(config->fd, SNDCTL_DSP_GETCAPS, &config->audio_info.caps) < 0)
98 err(1, "Unable to get capabilities");
99
100 /* Check if device supports triggering */
101 if (!(config->audio_info.caps & PCM_CAP_TRIGGER))
102 errx(1, "Device doesn't support triggering!\n");
103
104 /* Handle memory mapped mode */
105 if (config->mmap) {
106 if (!(config->audio_info.caps & PCM_CAP_MMAP))
107 errx(1, "Device doesn't support mmap mode!\n");
108 tmp = 0;
109 if (ioctl(config->fd, SNDCTL_DSP_COOKEDMODE, &tmp) < 0)
110 err(1, "Unable to set cooked mode");
111 }
112
113 /* Set sample format */
114 if (ioctl(config->fd, SNDCTL_DSP_SETFMT, &config->format) < 0)
115 err(1, "Unable to set sample format");
116
117 /* Set sample channels */
118 if (ioctl(config->fd, SNDCTL_DSP_CHANNELS, &config->audio_info.max_channels) < 0)
119 err(1, "Unable to set channels");
120
121 /* Set sample rate */
122 if (ioctl(config->fd, SNDCTL_DSP_SPEED, &config->sample_rate) < 0)
123 err(1, "Unable to set sample rate");
124
125 /* Calculate sample size */
126 switch (config->format) {
127 case AFMT_S8:
128 case AFMT_U8:
129 config->sample_size = 1;
130 break;
131 case AFMT_S16_BE:
132 case AFMT_S16_LE:
133 case AFMT_U16_BE:
134 case AFMT_U16_LE:
135 config->sample_size = 2;
136 break;
137 case AFMT_S24_BE:
138 case AFMT_S24_LE:
139 case AFMT_U24_BE:
140 case AFMT_U24_LE:
141 config->sample_size = 3;
142 break;
143 case AFMT_S32_BE:
144 case AFMT_S32_LE:
145 case AFMT_U32_BE:
146 case AFMT_U32_LE:
147 case AFMT_F32_BE:
148 case AFMT_F32_LE:
149 config->sample_size = 4;
150 break;
151 default:
152 errx(1, "Invalid audio format %d", config->format);
153 break;
154 }
155
156 /*
157 * Set fragment and sample size. This part is optional as OSS has
158 * default values. From the kernel's perspective, there are few things
159 * OSS developers should be aware of:
160 *
161 * - For each sound(4)-created channel, there is a software-facing
162 * buffer, and a hardware-facing one.
163 * - The sizes of the buffers can be listed in the console with "sndctl
164 * swbuf hwbuf".
165 * - OSS ioctls only concern software-facing buffer fragments, not
166 * hardware.
167 *
168 * For USB sound cards, the block size is set according to the
169 * hw.usb.uaudio.buffer_ms sysctl, meaning 2ms at 48kHz gives 0.002 *
170 * 48000 = 96 samples per block. Block size should be set as multiple
171 * of 96, in this case. The OSS driver insists on reading/writing a
172 * certain number of samples at a time, one fragment full of samples.
173 * It is bound to do so at a fixed time frame, to avoid under- and
174 * overruns during communication with the hardware.
175 */
176 config->buffer_info.fragments = 2;
177 tmp = size2exp(config->sample_size * config->audio_info.max_channels);
178 tmp = ((config->buffer_info.fragments) << 16) | tmp;
179 if (ioctl(config->fd, SNDCTL_DSP_SETFRAGMENT, &tmp) < 0)
180 err(1, "Unable to set fragment size");
181
182 /* Get buffer info */
183 if ((config->mode & O_ACCMODE) == O_RDONLY)
184 request = SNDCTL_DSP_GETISPACE;
185 if (ioctl(config->fd, request, &config->buffer_info) < 0)
186 err(1, "Unable to get buffer info");
187 if (config->buffer_info.fragments < 1)
188 config->buffer_info.fragments = config->buffer_info.fragstotal;
189 if (config->buffer_info.bytes < 1)
190 config->buffer_info.bytes = config->buffer_info.fragstotal * config->buffer_info.fragsize;
191 if (config->buffer_info.bytes < 1) {
192 errx(1, "OSS buffer error: buffer size can not be %d\n",
193 config->buffer_info.bytes);
194 }
195 config->sample_count = config->buffer_info.bytes / config->sample_size;
196 config->chsamples = config->sample_count / config->audio_info.max_channels;
197 config->buf = malloc(config->buffer_info.bytes);
198
199 printf("bytes: %d, fragments: %d, fragsize: %d, fragstotal: %d, "
200 "samples: %d\n",
201 config->buffer_info.bytes, config->buffer_info.fragments,
202 config->buffer_info.fragsize, config->buffer_info.fragstotal,
203 config->sample_count);
204
205 /* Set the trigger */
206 switch (config->mode & O_ACCMODE) {
207 case O_RDONLY:
208 tmp = PCM_ENABLE_INPUT;
209 break;
210 case O_WRONLY:
211 tmp = PCM_ENABLE_OUTPUT;
212 break;
213 case O_RDWR:
214 tmp = PCM_ENABLE_INPUT | PCM_ENABLE_OUTPUT;
215 break;
216 default:
217 errx(1, "Invalid mode %d", config->mode);
218 break;
219 }
220 if (ioctl(config->fd, SNDCTL_DSP_SETTRIGGER, &tmp) < 0)
221 err(1, "Failed to set trigger");
222 }
223