Freescale Semiconductor i.MX51 EVK Reference Manual Download

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MC13892 Digitizer Driver

i.MX51 EVK Linux Reference Manual

5-2

Freescale Semiconductor

The PMIC Digitizer Driver supports the following features for supporting a touch panel device:

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Selects either a single ADC input channel or an entire group of input channels to be converted

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Specifies high and low level thresholds for each ADC conversion

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Starts an ADC conversion by issuing the appropriate start conversion command

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Starts an ADC conversion immediately following the rising edge of the ADTRIG input line or after
a predefined delay following the rising edge

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Enable/disables hardware interrupts for all ADC-related event notifications

•

Provides an interrupt handler routine that receives and properly handles all ADC
end-of-conversion or exceeded high/low level threshold event notifications

•

Other device drivers register/deregister additional callback functions to provide custom handling
of all ADC-related event notifications

•

Provides a read-only device interface for passing touchpanel (X,Y) coordinates and pressure
measurements to applications

•

Provides the ability to read out one or more ADC conversion results

•

Implements the appropriate input scaling equations so that the ADC results are correct

•

Specifies the delay between successive ADC conversion operations, if supported by the PMIC. For
PMIC chips that do not support this feature, the device driver returns a NOT_SUPPORTED status

•

Provides support for a pulse generator that is synchronized with the ADC conversion. For PMIC
chips that do not support this feature, returns a NOT_SUPPORTED status

•

Provides a complete IOCTL interface to initiate an ADC conversion operation and to return the
conversion results

•

Provides support for a polling method to detect when the ADC conversion has been completed

This digitizer driver is not responsible for any additional ADC-related activities such as battery level or
USB ID handling. Such functions are handled by other PMIC-related device drivers. Also, this device
driver is not responsible for SPI bus arbitration configuration. The appropriate arbitration settings that are
required in order for this device driver to work properly are expected to have been set during the system
boot process.

5.2

Software Operation

Most of the required operations for this device driver simply involve writing the correct configuration
settings to the appropriate PMIC control registers. This can be done by using the APIs that are provided
with the PMIC protocol driver.

Once an ADC conversion has been started, suspend the calling thread until the conversion has been
completed. Avoid using a busy loop since this negatively impacts processor and overall system
performance. Instead, the use of a wait queue offers a much better solution. Therefore, any potentially
time-consuming operations results in the calling thread being placed into a wait queue until the operation
is completed.

The PMIC ADC conversion can take a significant amount of time. The delay between a start of conversion
request and a conversion completed event may even be open ended, if the conversion is not started until
the appropriate external trigger signal is received. Therefore, all ADC conversion requests must be placed