Tks takashi....
The doubt comes from this block of code:
for (chn = 0; chn < channels; chn++) { if ((areas[chn].first % 8) != 0) { printf("areas[%i].first == %i, abortando...\n", chn, areas[chn].first); exit(EXIT_FAILURE); } //pega endereço e offset da area samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
if ((areas[chn].step % 16) != 0) { printf("areas[%i].step == %i, aborting...\n", chn, areas[chn].step); exit(EXIT_FAILURE); }
steps[chn] = areas[chn].step / 8; samples[chn] += offset * steps[chn]; }
first:
areas[chn].first % 8 ( I am using chn = 1). So for the only area that I have, if I get the value of the parameter 'first' isn't divisible by 8, the program exits. The same doubt happens with "areas[chn].step % 16" and "areas[chn].step / 8".
This is the parameter I am using:
static snd_pcm_format_t format = SND_PCM_FORMAT_S16; //sample format unsigned 16 bit endian
Perhaps with this practical example I can understand better.
Thanks for ur patient!
Tks!
-------------------
Guilherme Longo
Dept. Eng. da Computação Unaerp
Linux User - #484927
*Before Asking http://www.istf.com.br/?page=perguntas
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Takashi Iwai wrote:
At Fri, 26 Jun 2009 23:56:43 -0300, Guilherme wrote:
Takashi...
The base_address and the step sounds pretty clear to me.... just the offset I could not understand.
What the difference in being .first = 0 or .first = 2??? Could you provide please a more in depth explanation. I tried really hard find this but there is nothing related in the documentation.
area[0].addr = base_address; addr[0].first = 0; addr[0].step = 4; addr[1].addr = base_address; addr[1].first = 2; addr[1].step = 4;
P.S. being a stereo or a mono pipeline I understand... just the way the offset works that is not so clear to me.
Actually, the non-interleaved formats can be represented also with a single base_address (and is so in the actual implementation).
addr[0].addr = base_addr; addr[0].first = 0; addr[0].step = 2; addr[1].addr = base_addr; addr[1].first = mono_buffer_len; addr[1].step = 2; addr[2].addr = base_addr; addr[2].first = mono_buffer_len * 2; addr[2].step = 2; ...
The "first" is the offset of the first sample. The address of the first sample of the channel is simply calculated as addr + first. This is because just we want to keep the base address same to all channels as much as possible especially in mmap mode.
Takashi