AM623: GPMC_FCLK

Hello Davey

Thank you for the query and no worries.

Davey Thomas said:

Is there a way to set GPMC_FCLK to 43.75 MHz?

Are you looking to set the specific frequency that you listed above?

Regards,

Sreenivasa

Yes, I need the GPMC Bus transactions to be clocked at 43.75 Mhz.  According to the datasheet and TRFM the GPMC is clocked with the GPMC_FCLK.

Hello Davey

Thankk you for the inputs.

Based on the inputs received, the frequency you are looking to generate may not be feasible using the available dividers.

Regards,

Sreenivasa

Hi Kallikuppa,

Can I use the EXT_REFCLK1 input in addition to the other required clock inputs?  The thought here is to use the EXT_REFCLK1 with a 43.75 MHz oscillator and use it for the GPMC module only.

Regards,

Davey

Hello Davey

Thank you. 

I am not able to understand your approach. Would you mind providing some additional details.

Is the plan to provide 43.75 MHz clock externally.

Regards,

Sreenivasa

Hi Sreenivasa,

I just looked at the AM625/AM623 Schematic Design and Review Checklist.  You need to use a 25 MHz crystal or clock on MCU_OSC0_XI / MCU_OSC0_XO a 32.768 kHz crystal or clock on WKUP_LFOSC0_XI / WKUP_LFOSC0_XO.  I was wondering if I could use a 43.75 MHz oscillator on the EXT_REFCLK1 clock input and route it to the GPMC using one of the clock muxes in the clocktree.  However, according to the checklist list the EXT_REFCLK1 is only selectable for the DMTIMER WDT MCAN and CPTS modules.  Could you please verify this? 

I'm trying to replace a very old processor (MPC875) whereas we used a 43.75 MHz main clock and 32.768 kHz clock so our address and data bus is clocked at 43.75 MHz.  The issue is the address and databus connect to a CPLD and many FPGA's so it would mean major code re-write to use a clock other than 43.75 MHz for this bus.  We are also investigating a clock domain crossing (CDC) in the CPLD's and FPGA's but of course we would like to avoid that as well if possible.

Regards,

Davey

Hello Davey

Thank you. 

Davey Thomas said:

I was wondering if I could use a 43.75 MHz oscillator on the EXT_REFCLK1 clock input and route it to the GPMC using one of the clock muxes in the clocktree.  However, according to the checklist list the EXT_REFCLK1 is only selectable for the DMTIMER WDT MCAN and CPTS modules.  Could you please verify this? 

I think so.

I can check internally but do not expect to have a quick answer.

Regards,

Sreenivasa