WM8281ECSSLASHR datasheet(266/392 Pages) CIRRUS

266 / 392 page

WM8281

266

Rev 4.0

The required control sequence for disabling SYSCLK is summarised below:



Disable all SYSCLK-associated functions (inputs, outputs, digital core)



Set SYSCLK_ENA = 0



Wait until SYSCLK_ENA_LOW = 1 (or wait for the corresponding IRQ/GPIO event)

The ASYNC_CLK_SRC register is used to select the ASYNCCLK source, as described in Table 101.

The source may be MCLKn, AIFnBCLK or FLLn. If one of the Frequency Locked Loop (FLL) circuits is

selected as the source, then the relevant FLL must be enabled and configured, as described later.

The ASYNC_CLK_FREQ register is set according to the frequency of the selected ASYNCCLK

source.

The ASYNCCLK-referenced circuits within the digital core are clocked at a dynamically-controlled

rate, limited by the ASYNCCLK frequency itself. For maximum signal mixing and processing capacity,

it is recommended that the highest possible ASYNCCLK frequency is configured.

The ASYNC_SAMPLE_RATE_n registers are set according to the sample rate(s) of any audio

interface that is not synchronised to the SYSCLK clock domain.

The ASYNCCLK signal is enabled by the register bit ASYNC_CLK_ENA. The applicable clock source

(MCLKn, AIFnBCLK or FLLn) must be enabled before setting ASYNC_CLK_ENA=1. This bit should

be set to 0 when reconfiguring the clock sources (see below for additional requirements when setting

ASYNC_CLK_ENA=0).

When disabling ASYNCCLK, note that all of the input, output or digital core functions associated with

the ASYNCCLK clock domain must be disabled before setting ASYNC_CLK_ENA=0.

When ‘0’ is written to ASYNC_CLK_ENA, the host processor must wait until the WM8281 has shut

down the associated functions before issuing any other register write commands. The ASYNCCLK

Enable status can be polled via the ASYNC_CLK_ENA_LOW_STS bit (see Table 98), or else

monitored using the Interrupt or GPIO functions.

The ASYNCCLK Enable status is an input to the Interrupt control circuit and can be used to trigger an

Interrupt event -

see “Interrupts”. The corresponding Interrupt event indicates that the WM8281 has

shut down the ASYNCCLK functions and is ready to accept register write commands.

The ASYNCCLK Enable status can be output directly on a GPIO pin as an external indication of the

ASYNCCLK

status. See “General Purpose Input / Output” to configure a GPIO pin for this function.

The required control sequence for disabling ASYNCCLK is summarised below:



Disable all ASYNCCLK-associated functions (inputs, outputs, digital core)



Set ASYNCCLK_ENA = 0



Wait until ASYNCCLK_ENA_LOW = 1 (or wait for the corresponding IRQ/GPIO event)

The SYSCLK (and ASYNCCLK, when applicable) clocks must be configured and enabled before any

audio path is enabled.

The WM8281 performs automatic checks to confirm that the SYSCLK and ASYNCCLK frequencies

are high enough to support the commanded signal paths and processing functions. If an attempt is

made to enable a signal path or processing function, and there are insufficient SYSCLK or

ASYNCCLK cycles to support it, then the attempt will be unsuccessful. (Note that any signal paths

that are already active will not be affected under these circumstances.)

An Underclocked Error condition is where there are insufficient clock cycles for the requested

functionality, and increasing the SYSCLK or ASYNCCLK frequency (as applicable) should allow the

selected configuration to be supported.

An Overclocked Error condition is where the requested functionality cannot be supported, as the

clocking requirements of the requested configuration exceed the device limits.

The SYSCLK Underclocked condition, ASYNCCLK Underclocked condition, and other Clocking Error

conditions

can be monitored using the GPIO and/or Interrupt functions. See “General Purpose Input /

Output

” and “Interrupts” for further details.

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