[meta-xilinx] Zynq XADC

[MUGRIDGE Robin]

> -----Original Message-----
> From: Sören Brinkmann [mailto:soren.brinkmann at xilinx.com]
> Sent: 18 May 2015 16:05
> To: MUGRIDGE Robin
> Cc: meta-xilinx at yoctoproject.org
> Subject: Re: [meta-xilinx] Zynq XADC
> 
> On Mon, 2015-05-18 at 02:50PM +0000, MUGRIDGE Robin wrote:
> >
> >
> >
> >
> >
> >
> >
> >
> >    > -----Original Message-----
> >
> >    > From: Sören Brinkmann [mailto:soren.brinkmann at xilinx.com]
> >
> >    > Sent: 18 May 2015 15:42
> >
> >    > To: MUGRIDGE Robin
> >
> >    > Cc: meta-xilinx at yoctoproject.org
> >
> >    > Subject: Re: [meta-xilinx] Zynq XADC
> >
> >    >
> >
> >    > On Mon, 2015-05-18 at 11:31AM +0000, MUGRIDGE Robin wrote:
> >
> >    > >    Hi,
> >
> >    > >
> >
> >    > >
> >
> >    > >
> >
> >    > >    I am having an issue trying to use the Zynq XADC after a linux
> >    reboot.  On
> >
> >    > >    power up, I can access the XADC in the FSBL.  If I stop the boot in
> >    u-boot
> >
> >    > >    and issue a reset command, I can still access the XADC from the
> >    FSBL.
> >
> >    > >    However, if I let linux start and then issue a reboot command, the
> >    XADC
> >
> >    > no
> >
> >    > >    longer works in the FSBL (the XAdcPs_SelfTest function fails – all
> >    XADC
> >
> >    > >    register reads return 0).
> >
> >    > >
> >
> >    > >
> >
> >    > >
> >
> >    > >    I’m using Dizzy.  If it has anything to do with it, I’m not
> >    configuring
> >
> >    > >    the PL at boot – this is done after linux starts.
> >
> >    > >
> >
> >    > >
> >
> >    > >
> >
> >    > >    Is there anything I need to do to allow the XADC to work after
> >    linux has
> >
> >    > >    been running?
> >
> >    >
> >
> >    > Are you accessing the device through its driver or some other path? The
> >
> >    > symptoms sound suspiciously like the device's clock isn't enabled.
> >
> >    > Usually the driver is supposed to handle that though. Could you check
> >    the
> >
> >    > state of the PCAP clock in /sys/kernel/debug/clk/clk_summary?
> >
> >    >
> >
> >
> >
> >    I haven't (yet) tried to access the XADC from linux - I will need to do
> >    this, so if enabling it in linux is likely to help a pointer on what to do
> >    would help!
> 
> Linux does disable all unused clocks after boot. So, if you don't have
> the XADC driver active in Linux, Linux is likely to disable the clock,
> which might explain the issue you see.
> If you're not running Linux while seeing the issue, check the
> state of the clock through the debugger or something by directly reading
> the clock control register (IIRC, PCAP_CLK_CTRL).
> 
> 

PCAP_CLK_CTRL is 0x00000501 in both working and failing cases.  I'll try to get the XADC driver in Linux going to see if that makes a difference.

>
> >
> >
> >    The only reference to the PCAP in clk_summary is...
> >
> >
> >
> >       clock                        enable_cnt  prepare_cnt  rate
> >    accuracy
> >
> >    ---------------------------------------------------------------------------------
> >
> >              pcap_mux              1           1            999999990  0
> >
> >                 pcap_div           1           1            199999998  0
> >
> >                    pcap            1           2            199999998  0
> 
> This looks good. The clock is enabled. If things look like this and the
> device doesn't work, something else must be wrong.
> 


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