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* TI - TSC ADC (Touschscreen and analog digital converter)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Required properties:
- child "tsc"
ti,wires: Wires refer to application modes i.e. 4/5/8 wire touchscreen
support on the platform.
ti,x-plate-resistance: X plate resistance
ti,coordinate-readouts: The sequencer supports a total of 16
programmable steps each step is used to
read a single coordinate. A single
readout is enough but multiple reads can
increase the quality.
A value of 5 means, 5 reads for X, 5 for
Y and 2 for Z (always). This utilises 12
of the 16 software steps available. The
remaining 4 can be used by the ADC.
ti,wire-config: Different boards could have a different order for
connecting wires on touchscreen. We need to provide an
8 bit number where in the 1st four bits represent the
analog lines and the next 4 bits represent positive/
negative terminal on that input line. Notations to
represent the input lines and terminals resoectively
is as follows:
AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
XP = 0, XN = 1, YP = 2, YN = 3.
- child "adc"
ti,adc-channels: List of analog inputs available for ADC.
AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
Optional properties:
- child "tsc"
ti,charge-delay: Length of touch screen charge delay step in terms of
ADC clock cycles. Charge delay value should be large
in order to avoid false pen-up events. This value
effects the overall sampling speed, hence need to be
kept as low as possible, while avoiding false pen-up
event. Start from a lower value, say 0x400, and
increase value until false pen-up events are avoided.
The pen-up detection happens immediately after the
charge step, so this does in fact function as a
hardware knob for adjusting the amount of "settling
time".
- child "adc"
ti,chan-step-opendelay: List of open delays for each channel of
ADC in the order of ti,adc-channels. The
value corresponds to the number of ADC
clock cycles to wait after applying the
step configuration registers and before
sending the start of ADC conversion.
Maximum value is 0x3FFFF.
ti,chan-step-sampledelay: List of sample delays for each channel
of ADC in the order of ti,adc-channels.
The value corresponds to the number of
ADC clock cycles to sample (to hold
start of conversion high).
Maximum value is 0xFF.
ti,chan-step-avg: Number of averages to be performed for each
channel of ADC. If average is 16 then input
is sampled 16 times and averaged to get more
accurate value. This increases the time taken
by ADC to generate a sample. Valid range is 0
average to 16 averages. Maximum value is 16.
Example:
tscadc: tscadc@44e0d000 {
compatible = "ti,am3359-tscadc";
tsc {
ti,wires = <4>;
ti,x-plate-resistance = <200>;
ti,coordiante-readouts = <5>;
ti,wire-config = <0x00 0x11 0x22 0x33>;
ti,charge-delay = <0x400>;
};
adc {
ti,adc-channels = <4 5 6 7>;
ti,chan-step-opendelay = <0x098 0x3ffff 0x098 0x0>;
ti,chan-step-sampledelay = <0xff 0x0 0xf 0x0>;
ti,chan-step-avg = <16 2 4 8>;
};
}
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