Hi Alan,
Thanks for the suggestion - I have GDB and J-Link and am using VS Code
as my IDE, which does have some "watch" limitations it seems :(
But I have found I was wrong about it being NuttX that's changing the
SFR register. It seems that U-boot doesn't set it despite being
configured for the 24MHz crystal I'm using. Some research suggests it
will only set the register in relation to USB (the usual reason for
wanting the 480MHz PLL to work) which is a shortcoming as getting a
clock that is an integer multiple of 8MHz for 1Mbit CANbus from the
usual 164MHz MCLK for this processor is a pain!
I will look to sorting U-boot config to get this to work, or may just
swap to a 12MHz crystal as used on the SAMA5D2 boards - not sure why the
eval board for the SAMA5D27 changed to using a 24MMhz crystal for no
good reason!
As always, thanks for taking the time to assist.
Regards,
Tim.
On 09/07/2021 17:30, Alan Carvalho de Assis wrote:
Hi Tim,
I don't know about the internal clock of SAMA5D27, but maybe some
other configuration is changing the SFR.
Do you have GDB working on your system? Maybe you can try to use
watchpoint at this register position, see here:
https://acassis.wordpress.com/2015/07/07/using-watchpoints-in-the-gdb-to-verify-register-access/
I hope it help you to discovery what is going on.
BR,
Alan
On 7/9/21, Tim <t...@jti.uk.com.invalid> wrote:
Hi,
Making slow progress getting MCAN sorted properly on my custom sama5d27
board and when clocking it from the "UPLL" clokc (an internal PLL used to
generate a 480MHz clock for the USB interfaces, and a useful clock for
higher speed CAN setups) I found that the CAN baud rate was out.
This is because there is a special function register (SFR) that has to be
set to reflect the crystal frequency used. This is correctly set by the
AT91
bootloader and/or Uboot (I can read it at the start of the bringup code OK)
but somewhere it is being changed to the wrong value again and I can't find
where - a grep for the relevant SFR register in all of the nuttx code
doesn't reveal anything (it only exists in my code or the sam_sfr header
file as far as I can see)
I have done a quick fix by re-writing the correct value in my bringup code
but that isn't the right way to sort this.
Any suggestions of how to find where/why/how this is being changed?
Thanks,
Tim.
