LPC18xx: CGU AUTOBLOCK bit

[naoa]

Hi,

I've found following updated notes about PLL1 settings in the latest LPC18xx User Manual.
However, our old products did not deal with this.

12.6.5.2 PLL1 control register
Table 123. PLL1_CTRL register (PLL1_CTRL, address 0x4005 0044) bit description
:
[1] When the PLL1 is enabled, set the AUTOBLOCK bit in the PLL1_CTRL register to 1. This bit
re-synchronizes the clock output during frequency changes that prevents glitches when switching clock
frequencies.

I changed the frequency of PLL 1 as shown below, but will glitch occur?
And, what happens to the CPU when glitch occurs?

Chip_Clock_SetBaseClock(CLK_BASE_MX, CLKIN_IRC, true, false);
Chip_Clock_EnableCrystal();
Chip_Clock_SetupMainPLLHz(CLKIN_CRYSTAL, 12000000, 180000000, 180000000); // note: PLL1 divide by 2
while(!Chip_Clock_MainPLLLocked());
Chip_Clock_SetBaseClock(CLK_BASE_MX, CLKIN_MAINPLL, true, false);

for(int delay=0; delay<= 1240*10; delay++);// Wait 50 us

LPC_CGU->PLL1_CTRL |= (1 << 7) ; /* DIRECT 90MHz -> 180MHz */

[jeremyzhou]

Hi 尚久 荒川,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
After having a review of your code, I found that you basically follow the steps which are illustrated in 12.2.1.2 Changing the BASE_M3_CLK after waking up from deep-sleep or power-down modes.
I'd like to if you can introduce the glitch you mentioned and I was wondering if you can share the demo which can replicate this phenomenon.

I'm looking forward to your reply.
Have a great day,
TIC

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[naoa]

Hi jeremyzhou, thank you very much for your fast and accurate reply.

My product is old.
I basically follow the procedure outlined in LPC18xx User manual Rev.2.8, 12.2.1.1 Changing the BASE_M3_CLK after power-up, reset, or deep power-down mode.
And, I am using the legacy version of LPCOpen v2.20.
v2.20 does not set the AUTOBLOCK bit in the Chip_Clock_SetupMainPLLHz function.

I have tested tens of thousands of times, but the problem has not occurred.
Is it unnecessary to set the AUTOBLOCK bit in my product?

[jeremyzhou · Accepted solution]

Hi 尚久 荒川,

Thanks for your reply.
I believe it's unnecessary to set the AUTO BLOCK bit (bit 11) after checking the various versions of LPCOpen library.

Hope this is clear.
Have a great day,
TIC

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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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