Open Sound System
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ioctl(fd, SNDCTL_DSP_GETOPTR, &ci);
The above code fragment lacks all error checks for clarity. Real world applications must always check for the errors and handle them as described below. Also most OSS ioctl calls will return information in the argument variable and it's usually necessary to check it too.
unsigned int bytesis the number of bytes played since the operation was started.
int blocksis the number of fragments played.
int ptris current playback pointer (between 0 and buffer_size-1).
See the Audio timing considerations section for more information about audio timing.
In mmap mode (only) the ptr field tells the location where the next sample will be playback. The blocks field tells how many fragments have been playback since the last time this call was made (can be used for overun detection).
This ioctl call should only be used when using mmap(). In normal applications it's practically useless. For example the bytes field will wrap uncontrolledly after one hour or 2^32 bytes have been playback.
Please look at the When OSS audio ioctl calls can be made section for information about DSP ioctl call ordering.
The return value from the OSS ioctl calls will be -1 if a fatal error occurred. Other values mean that the ioctl call was more or less successful. However in most cases the application must check the value returned in the argument to see what was the accepted value.
Please see the Possible error codes (errno) returned by OSS calls section for more info about the error codes returned by OSS.
|mmap_duplex.c||A simple sample program for doing dull duplex using mmap|
|mmap_test.c||A sample program for using mmap()|
|ioctl_test.c||This program has been used to verify that some of the ioctl calls work|