What freq XTAL is required to run XMOS L1 500Mhz core

[jagspaul]

What will be the PLL Multiplier and XTAL freq for XMOS L1 500 Mhz core to get full speed i.e. each core run at 125 Mhz.

regards
jags

[Bianco]

You can use 20MHz, 25MHz or other values, the PLL is programmable :)

[jagspaul]

Pll = 20 for m0 & m1 = 1
Xtal = 25mhz
then core freq is 20 * 25 = 500 mhz
Am i right bianco?

For xtal = 20mhz, pll value required 500/20 = 25
But i don't know how to program pll=25

Can you help me bianco?

Regards
Jags

[segher]

You do not program the PLL normally. You just set the correct external
clock frequency and the desired reference and core clock frequencies
in your XN file.

[jagspaul]

Please give me example of m0 & m1 pin connection and xn file configuration for run l1 core with 500mhz also give proper value of xtal.

I prefer 20 or 25 mhz xtal.

Regards
Jags

[Bianco]

For 20 MHz you can use:

Mode0 = 0, Mode1 = 1, initial boot frequency = 166MHz
Mode0 = 1, Mode1 = 1, initial boot frequency = 400MHz

For 25 MHz you can use:

Mode0 = 1, Mode1 = 0, initial boot frequency = 100MHz
Mode0 = 0, Mode1 = 1, initial boot frequency = 208MHz
Mode0 = 1, Mode1 = 1, initial boot frequency = 500MHz

If the initial frequency isnot 500 MHz, the PLL can be reprogrammed.
See seghers post above.

You can find this information in the datasheet.

[jon_ferg]

Hi,

You can't boot directly to 500MHz using the mode pins, PLL will be taken out of spec. The supported method is to use the XN file however, unless you are using a C5 part there is no guarantee that the device will operate reliably above 400MHz.

If you are using a 25MHz xtal set mode[1:0] == "10" ,and to "11" when using a 20MHz xtal. The tools will ensure you device is running at the desired frequency before your user code is run.

Jon

[Bianco]

My bad about the 500MHz boot freq, thanks Jonathan

[jagspaul]

For xmos l1 500mhz (c5) chip, can i use 500mhz initial boot freq?
M0,m1=[1,1] xtal=25mhz

Jags

[segher]

As jon_ferg says, you cannot do this. See http://www.xmos.com/published/xs1l_clk:

For boot mode 11, calling the input clock frequency "CLK", you have

Code: Select all

VCO freq = 60*CLK
system freq = 20*CLK

so your system freq will be fine (500MHz), but the VCO freq will be 1500MHz,
which is out of spec (maximum 1300MHz).