1. Change 'rt_uint8_t' type of cmd to 'int';
2. Add waitqueue;
3. Split device ipc header files;

    OXape reports: http://www.rt-thread.org/phpBB3/topic3939.html
          driver/ringbuffer: when data length is bigger than space length
          for rb, the read_index in rb is not update.
    When length > space, update the read_index, the bug can be fix, and
          works fine.

Add the APIs that will discard the old data when rb is full.

RT_RINGBUFFER_SIZE could mean "the size of the whole buffer", "the size
of the empty space" or "the size of the data". Moreover, it's never a
micro anymore. Change it to rt_ringbuffer_data_len before it's too late.
Also, RT_RINGBUFFER_EMPTY is changed to rt_ringbuffer_space_len.

The new implementation use the mirroring method to distinguish full
buffer and the empty buffer. It also support buffers of arbitrary size.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2529 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2431 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2384 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2314 bbd45198-f89e-11dd-88c7-29a3b14d5316

Add pipe, data queue implementation; Fix the issue which leaks one item in the available data of ring buffer.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2313 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2199 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2098 bbd45198-f89e-11dd-88c7-29a3b14d5316