CS47L35 datasheet(94/300 Pages) CIRRUS

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DS1085F3

CS47L35

4.5 DSP Peripheral Control

The event logger can be reset by writing 1 to EVENTLOGn_RST. Executing this function clears all the event logger status

flags and clears the contents of the FIFO buffer.

The associated timer (and time-stamp source) is selected using EVENTLOGn_TIME_SEL. Note that the event logger

must be disabled (EVENTLOGn_ENA = 0) when selecting the timer source.

4.5.2.3 Input Channel Configuration

The event logger allows up to 16 input channels to be configured for detection and logging. The EVENTLOGn_CHx_SEL

field selects the applicable input source for each channel (where x identifies the channel number, 1 to 16). The polarity

selection and debounce options are configured using the EVENTLOGn_CHx_POL and EVENTLOGn_CHx_DB bits

respectively.

The input channels can be enabled or disabled freely, using EVENTLOGn_CHx_ENA, without having to disable the event

logger entirely. An input channel must be disabled whenever the associated x_SEL, x_POL, or x_DB fields are written. It

is possible to reconfigure input channels while the event logger is enabled, provided the channels being reconfigured are

disabled when doing so.

The available input sources include GPIO inputs, external accessory status (jack, mic, sensors), and signals generated by

the integrated DSP cores. A list of the valid input sources for the event loggers is provided in Table 4-32. Note that, to log

both rising and falling events from any source, two separate input channels must be configured—one for each polarity.

If an input channel is configured for rising edge detection (EVENTLOGn_CHx_POL = 0), and the corresponding input

signal is asserted (Logic 1) at the time when the event logger is enabled, an event is logged in respect of this initial state.

Similarly, if an input channel is configured for falling edge detection, and is deasserted (Logic 0) when the event logger is

enabled, a corresponding event is logged. If rising and falling edges are both configured for detection, an event is always

logged in respect of the initial condition.

4.5.2.4 FIFO Buffer

Each event (signal transition) that meets the criteria of an enabled channel is written to the 16-stage FIFO buffer. The

buffer is filled cyclically, but does not overwrite unread data when full. An error condition occurs if the buffer fills up

completely.

Note that the FIFO behavior is not enforced or fully implemented in the device hardware, but assumes that a compatible

software implementation is in place. New events are written to the buffer in a cyclic manner, but the data can be read out

in any order, if desired. The designed FIFO behavior requires the software to update the read pointer (RPTR) in the

intended manner for smooth operation.

The entire contents of the 16-stage FIFO buffer can be accessed directly in the register map. Each FIFO index (y = 0 to

15) comprises the EVENTLOGn_FIFOy_ID (identifying the source signal of the associated log event), the EVENTLOGn_

FIFOy_POL (the polarity of the respective event transition), and the EVENTLOGn_FIFOy_TIME field (containing the 32-bit

time stamp from the associated timer).

The FIFO buffer is managed using EVENTLOGn_FIFO_WPTR and EVENTLOGn_FIFO_RPTR. The write pointer

(WPTR) field identifies the index location (0 to 15) in which the next event is logged. The read pointer (RPTR) field

identifies the index location of the first set of unread data, if any exists. Both of these fields are initialized to 0 when the

event logger is reset.

•If RPTR

 WPTR, the buffer contains new data. The number of new events is equal to the difference between the

two pointer values (WPTR – RPTR, allowing for wraparound beyond Index 15). For example, if WPTR = 12 and

RPTR = 8, this means that there are four unread data sets in the buffer, at index locations 8, 9, 10, and 11.

After reading the new data from the buffer, the RPTR value should be incremented by the corresponding amount

(e.g., increment by 4, in the example described above). Note that the RPTR value can either be incremented once

for each read, or can be incremented in larger steps after a batch read.

• If RPTR = WPTR, the buffer is either empty (0 events) or full (16 events). In this case, the status bits described in

Section 4.5.2.5 confirm the current status of the buffer.

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