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bcm2835 supports arbitrary positioning of channel data within a frame and thus is capable of supporting TDM modes. Since the driver is limited to 2-channel operations only TDM setups with exactly 2 active slots are supported. Logical TDM slot numbering follows the usual convention: For I2S-like modes, with a 50% duty-cycle frame clock, slots 0, 2, ... are transmitted in the first half of a frame, slots 1, 3, ... are transmitted in the second half. For DSP modes slot numbering is ascending: 0, 1, 2, 3, ... Channel position calculation has been refactored to use TDM info and moved out of hw_params. set_tdm_slot, set_bclk_ratio and hw_params now check more strictly if the configuration is valid. Illegal configurations like odd number of slots in I2S mode, data lengths exceeding slot width or frame sizes larger than the hardware limit of 1024 are rejected. Also hw_params now properly checks for errors from clk_set_rate. Allowed PCM formats are already guarded by stream constraints, thus the formats check in hw_params has been removed and data_length is now retrieved via params_width(). Also standard functions like snd_soc_params_to_bclk are now being used instead of manual calculations to make the code more readable. Special care has been taken to ensure that set_bclk_ratio works as before. The bclk ratio is mapped to a 2-channel TDM config with a slot width of half the ratio. In order to support odd ratios, which can't be expressed via a TDM config, the ratio (frame length) is stored and used by hw_params. Signed-off-by: Matthias Reichl <hias@horus.com> Signed-off-by: Mark Brown <broonie@kernel.org> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.