CS47L85 datasheet(147/370 Pages) CIRRUS

147 / 370 page

CS47L85

Rev 4.3

147

The FIFO buffer is managed using the EVENTLOGn_FIFO_WPTR and EVENTLOGn_FIFO_RPTR registers. The Write

Pointer (WPTR) field identifies the index location (0 to 15) in which the next event will be 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 initialised to 0 when the

Event Logger is reset.

If RPTR <> WPTR, then the buffer contains new data. The number of new events is equal to the difference between the two

pointer values (WPTR - RPTR, allowing for wrap-around beyond index 15). For example, if WPTR = 12 and RPTR = 8, this

means that there are 4 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, then the buffer is either empty (0 events) or full (16 events). In this case, the status bits described below

will confirm the current status of the buffer.

The EVENTLOGn_NOT_EMPTY bit indicates whether the FIFO buffer is empty. When this bit is set, it indicates one or more

new sets of data in the FIFO.

The EVENTLOGn_WMARK_STS bit indicates when the number of FIFO index locations available for new events reaches

a configurable threshold, known as the watermark level. The watermark level is held in the EVENTLOGn_WMARK register.

The EVENTLOGn_FULL bit indicates when the FIFO buffer is full. When this bit is set, it indicates that there are 16 sets of

new event data in the FIFO. Note that this does not mean that a buffer overflow condition has occurred; but further events

will not be logged or indicated until the buffer has been cleared.

Following

a ‘Buffer Full’ condition, the FIFO operation will resume as soon as the RPTR field has been updated to a new

value. Note that writing the same value to RPTR will not re-start the FIFO operation, even if the entire buffer contents have

been read. After all of the required data has been read from the buffer, the RPTR value should be set equal to the WPTR

value; note that an intermediate (different) value must always be written to the RPTR field in order to clear the ‘Buffer Full’

status and re-start the FIFO operation.

The Control Write Sequencer is automatically triggered whenever the NOT_EMPTY status of the Event Log buffer is

asserted.

A different control sequence may be configured for each of the Event Loggers. See “Control Write Sequencer” for

further details.

The Event Log status flags are inputs to the Interrupt control circuit and can be used to trigger an Interrupt event when the

respective FIFO condition (Full, Not Empty, or Watermark level) occurs -

see “Interrupts”.

The Event Log status can be output directly on a GPIO pin as an external indication of the Event Logger. Se

e “General

Purpose Input / Output

” to configure a GPIO pin for this function.

The Event Log NOT_EMPTY status can also be selected as a ‘Start’ trigger for DSP firmware execution. See “DSP Firmware

Control

” for further details.

CS47L85 Datasheet(PDF) 147 Page - Cirrus Logic

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