Re: [PATCH] ARM: dts: da850-lego-ev3: slow down A/DC as much as possible

[David Lechner]

On 9/25/18 1:04 AM, Sekhar Nori wrote:
> Hi David,
>
> On Monday 24 September 2018 07:01 AM, David Lechner wrote:
> > Due to the electrical design of the A/DC circuits on LEGO MINDSTORMS EV3,
> > if we are reading analog values as fast as possible (i.e. using DMA to
> > service the SPI) the A/DC chip will read incorrect values - as much as
> > 0.1V off when the SPI is running at 10MHz. (This has to do with the
> > capacitor charge time when channels are muxed in the A/DC.)
>
> So you believe this is an issue with the board design rather than the
> limitation of the ADC chip itself? Because if its the later, the fix
> should be in the driver instead.

It is the board design. There are external 4.7k series resistors that 
make the RC charge time so long.

> > Both of these patches mentioned have been picked up in the respective
> > subsystems.
>
> Is this needed for the -rc cycle or can wait for v4.20?

v4.20