C6748 456mhz to 375mhz

Craig Meyers

Intellectual 730 points

How do we setup the 456 to run at 375mhz?

over 14 years ago

0 Mukul Bhatnagar over 14 years ago

TI__Guru* 83855 points

Hi Craig

You should find the following PLL clocking spreadsheet tool helpful

http://processors.wiki.ti.com/index.php/Programming_PLL_Controllers_on_OMAP-L1x8/C674x/AM18xx

Based on your input frequency , you can get the values of what the device frequency will be.

The 456 MHz part can run at lower frequency w/o issues.

Regards

Mukul

0 Craig Meyers over 14 years ago in reply to Mukul Bhatnagar

Intellectual 730 points

I looked at the spreadsheet noted in the article. I'm curious how, specifically, we would clock the 456 mhz DSP to run at 375mhz. The spreadsheet indicates we can set CLKIN or OSCIN. But I noticed that if I change input voltage / operating point from 1.3 to 1.2 SYSCLK1 goes from (,456) to (,375). Is there a pin/parameter to set input voltage?

0 Tai Nguyen over 14 years ago in reply to Craig Meyers

TI__Expert 5955 points

Hi,

There is no pin/parameter to set input voltage to a lower/higher voltage.

Thanks,

Tai Nguyen

0 Craig Meyers over 14 years ago in reply to Tai Nguyen

Intellectual 730 points

I think I see how to do this in c6748 dsp sys ref guide sprugj7d section 7.3.10. If I want the 456 to clock at 375mhz it looks like I can modify PLLC0 Divider 1 Register (PLLDIV1). Setting the divider ration (RATIO) to 0.216 because 456 is 1.216 times 375. Can you confirm?

0 Craig Meyers over 14 years ago in reply to Craig Meyers

Intellectual 730 points

Please ignore last post - I just realized I only get a nibble for the ratio, So I only get integers for PLLDIV1.

The question remains. I cannot tell from the spreadsheet how to specifically run the 456mhz part at 375mhz.

0 Tai Nguyen over 14 years ago in reply to Craig Meyers

TI__Expert 5955 points

Hi,

The spreadsheet does not tell you how to run the 456Mhz part at 375Mhz but just to check if the PLL configuration is okay or not according to the input voltage, PREVDIV, PLLM, POSTDIV, PLLEN, PLLDIV1 inputs. If these inputs are set as in the spreadsheet, the device should just work at that speed.

For example, if you have a 456Mhz part and the input voltage is 1.2V and you use a 24Mhz clock and OSCIN for CLKMODE, set PLLM=31, POSTDIV=1, PLLEN=LOCK, PLLDIV1=1, you will see SYSCLK1 is set to 375, i.e. the DSP speed is set 375Mhz (DSP uses SYSCLK1) and SYSCLK6 is is set 375MHz, i.e. the ARM speed is set to 375Mhz (ARM uses SYSCLK6), then the device should run at 375Mhz. If PLLM is now changed to 32, the spreadsheet will flag "violation". But if the Input Voltage is changed to 1.3V then everything is okay again. It means the running the 456Mhz part with 1.3V volt core voltage the part can operate at 456Mhz.

Thanks,

Tai Nguyen

0 Craig Meyers over 14 years ago in reply to Tai Nguyen

Intellectual 730 points

Thanks Tai. I completely understand now!

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C6748 456mhz to 375mhz