topic Re: Unable to change VBAT0 OSCCTLA/OSCCTLB registers in MCX Microcontrollers

Unable to change VBAT0 OSCCTLA/OSCCTLB registers

Vagni — Sat, 07 Dec 2024 16:21:16 GMT

On the MCXN547 MCU I need to change run-time and enable the internal capacitor banks on the EXTAL and XTAL pins for tuning the OSC32kHz. But writing to VBAT0 OSCCTLA/OSCCTLB registers seems to not work: I get the same initial value when I read out the registers after writing a new value.

I tried to use the SDK VBAT_SetOscConfig() driver function, but I get the OSCCTLA/OSCCTLB registers unchanged.

Then I tried my own writing sequence:

/* unlock the OSC32K registers */ VBAT0->OSCLCKA &= ~VBAT_OSCLCKA_LOCK_MASK; VBAT0->OSCLCKB |= VBAT_OSCLCKB_LOCK_MASK; /* tmp32 is previously set with the new register value */ VBAT0->OSCCTLA = tmp32 & 0x000FFFFFUL; VBAT0->OSCCTLB = (~tmp32) & 0x000FFFFFUL; /* Wait for STATUSA[OSC_RDY] to set. */ while ((VBAT0->STATUSA & VBAT_STATUSA_OSC_RDY_MASK) == 0U) { } /* lock the OSC32K registers */ VBAT0->OSCLCKA |= VBAT_OSCLCKA_LOCK_MASK; VBAT0->OSCLCKB &= ~VBAT_OSCLCKB_LOCK_MASK;

My code is executed without errors, OSC32K keeps running, but again I get the OSCCTLA/OSCCTLB registers unchanged.

What is the right sequence to change OSCCTLA/OSCCTLB registers?

Re: Unable to change VBAT0 OSCCTLA/OSCCTLB registers

xiangjun_rong — Mon, 09 Dec 2024 09:28:17 GMT

Hi,

Pls refer to the section

/**
 * @brief Initialize the OSC 32K.
 * @param id : OSC 32 kHz output clock to specified modules
 * @return returns success or fail status.
 */
status_t CLOCK_SetupOsc32KClocking(uint32_t id)
{
/* Enable LDO */
 SCG0->LDOCSR |= SCG_LDOCSR_LDOEN_MASK | SCG_LDOCSR_VOUT_OK_MASK;
 
 VBAT0->OSCCTLA =
 (VBAT0->OSCCTLA & ~(VBAT_OSCCTLA_MODE_EN_MASK | VBAT_OSCCTLA_CAP_SEL_EN_MASK | VBAT_OSCCTLA_OSC_EN_MASK)) |
 VBAT_OSCCTLA_MODE_EN(0x2) | VBAT_OSCCTLA_OSC_EN_MASK | VBAT_OSCCTLA_OSC_EN_MASK;
 VBAT0->OSCCTLB = VBAT_OSCCTLB_INVERSE(0xDFF7E);
/* Wait for STATUSA[OSC_RDY] to set. */
while ((VBAT0->STATUSA & VBAT_STATUSA_OSC_RDY_MASK) == 0U)
 {
 }
 VBAT0->OSCLCKA = VBAT_OSCLCKA_LOCK_MASK;
 VBAT0->OSCLCKB &= ~VBAT_OSCLCKA_LOCK_MASK;
 
 VBAT0->OSCCLKE |= VBAT_OSCCLKE_CLKE(id);
 
/* De-initializes the SCG ROSC */
 SCG0->ROSCCSR = SCG_ROSCCSR_ROSCERR_MASK;
 
/* Unlock ROSCCSR */
 SCG0->ROSCCSR &= ~SCG_ROSCCSR_LK_MASK;
 
/* Enable SOSC clock monitor and Enable ROSC */
 SCG0->ROSCCSR |= SCG_ROSCCSR_ROSCCM_MASK;
 
/* Wait for ROSC clock to be valid. */
while ((SCG0->ROSCCSR & SCG_ROSCCSR_ROSCVLD_MASK) == 0U)
 {
 }
 
 s_Xtal32_Freq = 32768U;
 
return kStatus_Success;
}
 
Hope it can help you
BR
XiangJun Rong

Re: Unable to change VBAT0 OSCCTLA/OSCCTLB registers

Vagni — Thu, 12 Dec 2024 10:25:32 GMT

Hi XiangJun Rong,

I do call CLOCK_SetupOsc32KClocking() to init the OSC32K, then run-time I need to call VBAT_SetOscConfig() to config the Crystal Load Capacitance.

CLOCK_SetupOsc32KClocking() locks OSCCTLA/OSCCTLB registers after its writing, without any previous unlock. VBAT_SetOscConfig() does not unlock/lock those registers.

I think CLOCK_SetupOsc32KClocking() works only because OSCCTLA/OSCTLB start unlocked after the reset. The same for the CLOCK_SetupClk16KClocking() function.

So, after the very first OSCCTLA/OSCCTLB registers lock, how to unlock them for a changing?

Is it right to do the following unlock sequence prior any registers write access?

/* Unlock */ VBAT0->OSCLCKA &= ~VBAT_OSCLCKA_LOCK_MASK; VBAT0->OSCLCKB |= VBAT_OSCLCKB_LOCK_MASK;

After my registers writing, should I check STATUSA[CONFIG_DET] flag for any VBAT configuration error?

Re: Unable to change VBAT0 OSCCTLA/OSCCTLB registers

Vagni — Thu, 12 Dec 2024 13:49:43 GMT

From the MCXN Reference Manual I see VBAT registers can be locked until the next power-on reset (POR). Only after a POR the VBAT registers are unlocked. If the VBAT registers are locked, they cannot be unlocked writing the LOCK bit in the xxxLCKA/xxxLCKB registers.

You can write the LOCK bit in the xxxLCKA/xxxLCKB registers only for locking.

The SDK VBAT driver functions lock the VBAT registers, so the VBAT registers cannot be changed afterwards.

Then, I remarked the OSCCTLA/OSCCTLB registers locking in the CLOCK_SetupOsc32KClocking() function and now every call to VBAT_SetOscConfig() can successfully change the Crystal Load Capacitance.