Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
9 years, 5 months ago.
Freescale platform UART baud rate problem
I have an issue across the Freescale platforms with Serial (UART) baud rate not operating at 256k. Before the KL05Z was released earlier this year the Serial baud rate would work at this speed. After some code alterations and the board being released it not longer worked at this speed, maximum is now 128k. This is common to all the Freescale platforms I have, none appear to work above 128K.
In many applications this is probably not a problem, however I have a large number of 4DSystems Oled displays. Unfortunately these only have serial communication and need the maximum speed possible so as not to hold up other processing code. I have the system_ML05Z4.c code below that did work before the release. This code was changed to allow the crystal to work (which it does not in the code below). If I replace the latest file (in MBED-SRC) with this one and set to clock_setup (0) it works again. Bare in mind the clock source is 32Khz with both crystal and IRC (slow clock).
I have noticed the buss clock speed is different between crystal and IRC, perhaps the baud rate tolerances are to great as the speed goes up? But why would these be different, the clock frequency is the same?
Any input would be appreciated, perhaps from the guy that did the final release changes who may have the answer. However there must be a common factor across all the Freescale platforms.
system_ML05Z4.c
** ###################################################################
** Processors: MKL05Z32FK4
** MKL05Z32LC4
** MKL05Z32VLF4
**
** Compilers: ARM Compiler
** Freescale C/C++ for Embedded ARM
** GNU C Compiler
** IAR ANSI C/C++ Compiler for ARM
**
** Reference manual: KL05P48M48SF1RM, Rev.3, Sep 2012
** Version: rev. 1.6, 2013-04-11
**
** Abstract:
** Provides a system configuration function and a global variable that
** contains the system frequency. It configures the device and initializes
** the oscillator (PLL) that is part of the microcontroller device.
**
** Copyright: 2013 Freescale, Inc. All Rights Reserved.
**
** http: www.freescale.com
** mail: support@freescale.com
**
** Revisions:
** - rev. 1.0 (2012-06-08)
** Initial version.
** - rev. 1.1 (2012-06-21)
** Update according to reference manual rev. 1.
** - rev. 1.2 (2012-08-01)
** Device type UARTLP changed to UART0.
** Missing PORTB_IRQn interrupt number definition added.
** - rev. 1.3 (2012-10-04)
** Update according to reference manual rev. 3.
** - rev. 1.4 (2012-11-22)
** MCG module - bit LOLS in MCG_S register renamed to LOLS0.
** NV registers - bit EZPORT_DIS in NV_FOPT register removed.
** - rev. 1.5 (2013-04-05)
** Changed start of doxygen comment.
** - rev. 1.6 (2013-04-11)
** SystemInit methods updated with predefined initialization sequence.
**
** ###################################################################
*/
/*!
* @file MKL05Z4
* @version 1.6
* @date 2013-04-11
* @brief Device specific configuration file for MKL05Z4 (implementation file)
*
* Provides a system configuration function and a global variable that contains
* the system frequency. It configures the device and initializes the oscillator
* (PLL) that is part of the microcontroller device.
*/
#include <stdint.h>
#include "MKL05Z4.h"
#define DISABLE_WDOG 1
#define CLOCK_SETUP 0
/* Predefined clock setups
0 ... Multipurpose Clock Generator (MCG) in FLL Engaged Internal (FEI) mode
Reference clock source for MCG module is the slow internal clock source 32.768kHz
Core clock = 41.94MHz, BusClock = 20.97MHz
1 ... Multipurpose Clock Generator (MCG) in FLL Engaged External (FEE) mode
Reference clock source for MCG module is an external crystal 32.768kHz
Core clock = 47.97MHz, BusClock = 23.98MHz
2 ... Multipurpose Clock Generator (MCG) in FLL Bypassed Low Power Internal (BLPI) mode
Core clock/Bus clock derived directly from an fast internal 4MHz clock with no multiplication
Core clock = 4MHz, BusClock = 4MHz
*/
/*----------------------------------------------------------------------------
Define clock source values
*----------------------------------------------------------------------------*/
#if (CLOCK_SETUP == 0)
#define CPU_XTAL_CLK_HZ 32768u /* Value of the external crystal or oscillator clock frequency in Hz */
#define CPU_INT_SLOW_CLK_HZ 32768u /* Value of the slow internal oscillator clock frequency in Hz */
#define CPU_INT_FAST_CLK_HZ 4000000u /* Value of the fast internal oscillator clock frequency in Hz */
#define DEFAULT_SYSTEM_CLOCK 41943040u /* Default System clock value */
#elif (CLOCK_SETUP == 1)
#define CPU_XTAL_CLK_HZ 32768u /* Value of the external crystal or oscillator clock frequency in Hz */
#define CPU_INT_SLOW_CLK_HZ 32768u /* Value of the slow internal oscillator clock frequency in Hz */
#define CPU_INT_FAST_CLK_HZ 4000000u /* Value of the fast internal oscillator clock frequency in Hz */
#define DEFAULT_SYSTEM_CLOCK 47972352u /* Default System clock value */
#elif (CLOCK_SETUP == 2)
#define CPU_XTAL_CLK_HZ 32768u /* Value of the external crystal or oscillator clock frequency in Hz */
#define CPU_INT_SLOW_CLK_HZ 32768u /* Value of the slow internal oscillator clock frequency in Hz */
#define CPU_INT_FAST_CLK_HZ 4000000u /* Value of the fast internal oscillator clock frequency in Hz */
#define DEFAULT_SYSTEM_CLOCK 4000000u /* Default System clock value */
#endif /* (CLOCK_SETUP == 2) */
/* ----------------------------------------------------------------------------
-- Core clock
---------------------------------------------------------------------------- */
uint32_t SystemCoreClock = DEFAULT_SYSTEM_CLOCK;
/* ----------------------------------------------------------------------------
-- SystemInit()
---------------------------------------------------------------------------- */
void SystemInit (void) {
#if (DISABLE_WDOG)
/* Disable the WDOG module */
/* SIM_COPC: COPT=0,COPCLKS=0,COPW=0 */
SIM->COPC = (uint32_t)0x00u;
#endif /* (DISABLE_WDOG) */
#if (CLOCK_SETUP == 0)
/* SIM->CLKDIV1: OUTDIV1=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,OUTDIV4=1,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0 */
SIM->CLKDIV1 = (SIM_CLKDIV1_OUTDIV1(0x00) | SIM_CLKDIV1_OUTDIV4(0x01)); /* Update system prescalers */
/* Switch to FEI Mode */
/* MCG->C1: CLKS=0,FRDIV=0,IREFS=1,IRCLKEN=1,IREFSTEN=0 */
MCG->C1 = MCG_C1_CLKS(0x00) |
MCG_C1_FRDIV(0x00) |
MCG_C1_IREFS_MASK |
MCG_C1_IRCLKEN_MASK;
/* MCG->C2: LOCRE0=0,??=0,RANGE0=0,HGO0=0,EREFS0=0,LP=0,IRCS=0 */
MCG->C2 = MCG_C2_RANGE0(0x00);
/* MCG_C4: DMX32=0,DRST_DRS=1 */
MCG->C4 = (uint8_t)((MCG->C4 & (uint8_t)~(uint8_t)(
MCG_C4_DMX32_MASK |
MCG_C4_DRST_DRS(0x02)
)) | (uint8_t)(
MCG_C4_DRST_DRS(0x01)
));
/* OSC0->CR: ERCLKEN=1,??=0,EREFSTEN=0,??=0,SC2P=0,SC4P=0,SC8P=0,SC16P=0 */
OSC0->CR = OSC_CR_ERCLKEN_MASK;
while((MCG->S & MCG_S_IREFST_MASK) == 0x00U) { /* Check that the source of the FLL reference clock is the internal reference clock. */
}
while((MCG->S & 0x0CU) != 0x00U) { /* Wait until output of the FLL is selected */
}
#elif (CLOCK_SETUP == 1)
/* SIM->SCGC5: PORTA=1 */
SIM->SCGC5 |= SIM_SCGC5_PORTA_MASK; /* Enable clock gate for ports to enable pin routing */
/* SIM->CLKDIV1: OUTDIV1=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,OUTDIV4=1,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0 */
SIM->CLKDIV1 = (SIM_CLKDIV1_OUTDIV1(0x00) | SIM_CLKDIV1_OUTDIV4(0x01)); /* Update system prescalers */
/* PORTA->PCR[3]: ISF=0,MUX=0 */
PORTA->PCR[3] &= (uint32_t)~(uint32_t)((PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x07)));
/* PORTA->PCR[4]: ISF=0,MUX=0 */
PORTA->PCR[4] &= (uint32_t)~(uint32_t)((PORT_PCR_ISF_MASK | PORT_PCR_MUX(0x07)));
/* Switch to FEE Mode */
/* MCG->C2: LOCRE0=0,??=0,RANGE0=0,HGO0=0,EREFS0=1,LP=0,IRCS=0 */
MCG->C2 = (MCG_C2_RANGE0(0x00) | MCG_C2_EREFS0_MASK);
/* OSC0->CR: ERCLKEN=1,??=0,EREFSTEN=0,??=0,SC2P=0,SC4P=0,SC8P=0,SC16P=0 */
OSC0->CR = OSC_CR_ERCLKEN_MASK;
/* MCG->C1: CLKS=0,FRDIV=0,IREFS=0,IRCLKEN=1,IREFSTEN=0 */
MCG->C1 = (MCG_C1_CLKS(0x00) | MCG_C1_FRDIV(0x00) | MCG_C1_IRCLKEN_MASK);
/* MCG->C4: DMX32=1,DRST_DRS=1 */
MCG->C4 = (uint8_t)((MCG->C4 & (uint8_t)~(uint8_t)(
MCG_C4_DRST_DRS(0x02)
)) | (uint8_t)(
MCG_C4_DMX32_MASK |
MCG_C4_DRST_DRS(0x01)
));
while((MCG->S & MCG_S_IREFST_MASK) != 0x00U) { /* Check that the source of the FLL reference clock is the external reference clock. */
}
while((MCG->S & 0x0CU) != 0x00U) { /* Wait until output of the FLL is selected */
}
#elif (CLOCK_SETUP == 2)
/* SIM->CLKDIV1: OUTDIV1=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,OUTDIV4=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0,??=0 */
SIM->CLKDIV1 = (SIM_CLKDIV1_OUTDIV1(0x00) | SIM_CLKDIV1_OUTDIV4(0x00)); /* Update system prescalers */
/* MCG->SC: FCRDIV=0 */
MCG->SC &= (uint8_t)~(uint8_t)(MCG_SC_FCRDIV(0x07));
/* Switch to FBI Mode */
/* MCG->C1: CLKS=1,FRDIV=0,IREFS=1,IRCLKEN=1,IREFSTEN=0 */
MCG->C1 = MCG_C1_CLKS(0x01) |
MCG_C1_FRDIV(0x00) |
MCG_C1_IREFS_MASK |
MCG_C1_IRCLKEN_MASK;
/* MCG->C2: LOCRE0=0,??=0,RANGE0=0,HGO0=0,EREFS0=0,LP=0,IRCS=1 */
MCG->C2 = (MCG_C2_RANGE0(0x00) | MCG_C2_IRCS_MASK);
/* MCG->C4: DMX32=0,DRST_DRS=0 */
MCG->C4 &= (uint8_t)~(uint8_t)((MCG_C4_DMX32_MASK | MCG_C4_DRST_DRS(0x03)));
/* OSC0->CR: ERCLKEN=1,??=0,EREFSTEN=0,??=0,SC2P=0,SC4P=0,SC8P=0,SC16P=0 */
OSC0->CR = OSC_CR_ERCLKEN_MASK;
while((MCG->S & MCG_S_IREFST_MASK) == 0x00U) { /* Check that the source of the FLL reference clock is the internal reference clock. */
}
while((MCG->S & 0x0CU) != 0x04U) { /* Wait until internal reference clock is selected as MCG output */
}
/* Switch to BLPI Mode */
/* MCG->C2: LOCRE0=0,??=0,RANGE0=0,HGO0=0,EREFS0=0,LP=1,IRCS=1 */
MCG->C2 = (MCG_C2_RANGE0(0x00) | MCG_C2_LP_MASK | MCG_C2_IRCS_MASK);
while((MCG->S & MCG_S_IREFST_MASK) == 0x00U) { /* Check that the source of the FLL reference clock is the internal reference clock. */
}
while((MCG->S & MCG_S_IRCST_MASK) == 0x00U) { /* Check that the fast external reference clock is selected. */
}
#endif /* (CLOCK_SETUP == 2) */
}
/* ----------------------------------------------------------------------------
-- SystemCoreClockUpdate()
---------------------------------------------------------------------------- */
void SystemCoreClockUpdate (void) {
uint32_t MCGOUTClock; /* Variable to store output clock frequency of the MCG module */
uint8_t Divider;
if ((MCG->C1 & MCG_C1_CLKS_MASK) == 0x0u) {
/* Output of FLL is selected */
if ((MCG->C1 & MCG_C1_IREFS_MASK) == 0x0u) {
/* External reference clock is selected */
MCGOUTClock = CPU_XTAL_CLK_HZ; /* System oscillator drives MCG clock */
Divider = (uint8_t)(1u << ((MCG->C1 & MCG_C1_FRDIV_MASK) >> MCG_C1_FRDIV_SHIFT));
MCGOUTClock = (MCGOUTClock / Divider); /* Calculate the divided FLL reference clock */
} else { /* (!((MCG->C1 & MCG_C1_IREFS_MASK) == 0x0u)) */
MCGOUTClock = CPU_INT_SLOW_CLK_HZ; /* The slow internal reference clock is selected */
} /* (!((MCG->C1 & MCG_C1_IREFS_MASK) == 0x0u)) */
/* Select correct multiplier to calculate the MCG output clock */
switch (MCG->C4 & (MCG_C4_DMX32_MASK | MCG_C4_DRST_DRS_MASK)) {
case 0x0u:
MCGOUTClock *= 640u;
break;
case 0x20u:
MCGOUTClock *= 1280u;
break;
case 0x40u:
MCGOUTClock *= 1920u;
break;
case 0x60u:
MCGOUTClock *= 2560u;
break;
case 0x80u:
MCGOUTClock *= 732u;
break;
case 0xA0u:
MCGOUTClock *= 1464u;
break;
case 0xC0u:
MCGOUTClock *= 2197u;
break;
case 0xE0u:
MCGOUTClock *= 2929u;
break;
default:
break;
}
} else if ((MCG->C1 & MCG_C1_CLKS_MASK) == 0x40u) {
/* Internal reference clock is selected */
if ((MCG->C2 & MCG_C2_IRCS_MASK) == 0x0u) {
MCGOUTClock = CPU_INT_SLOW_CLK_HZ; /* Slow internal reference clock selected */
} else { /* (!((MCG->C2 & MCG_C2_IRCS_MASK) == 0x0u)) */
MCGOUTClock = CPU_INT_FAST_CLK_HZ / (1 << ((MCG->SC & MCG_SC_FCRDIV_MASK) >> MCG_SC_FCRDIV_SHIFT)); /* Fast internal reference clock selected */
} /* (!((MCG->C2 & MCG_C2_IRCS_MASK) == 0x0u)) */
} else if ((MCG->C1 & MCG_C1_CLKS_MASK) == 0x80u) {
/* External reference clock is selected */
MCGOUTClock = CPU_XTAL_CLK_HZ; /* System oscillator drives MCG clock */
} else { /* (!((MCG->C1 & MCG_C1_CLKS_MASK) == 0x80u)) */
/* Reserved value */
return;
} /* (!((MCG->C1 & MCG_C1_CLKS_MASK) == 0x80u)) */
SystemCoreClock = (MCGOUTClock / (1u + ((SIM->CLKDIV1 & SIM_CLKDIV1_OUTDIV1_MASK) >> SIM_CLKDIV1_OUTDIV1_SHIFT)));
}
Question relating to:
Last updated: 27 May 2019
The FRDM-KL05Z is an ultra-low-cost development platform enabled by the Kinetis L Series KL0x MCU family built on the ARM® Cortex™-M0+ processor. Features include easy access to MCU I/O, battery-ready, …
Be the first to answer this question.
I have reloaded the current Mbed file again and set to IRC (clock setup 0) and that does work. So there must be a problem with buss clock preescaler settings. Why would these be different with the same main clock rate?
Just tried IRC on the KL25Z and this also works at 256k. Is it possible the preescalers will not clock at the correct rate unless in IRC mode?
posted by Paul Staron 09 Nov 2014I actually have no idea why mode 0 and 1 aren't set to use same prescaler options to result in same frequency. I think it is a bit of luck that with the different clock the final baudrate is more accurate. However I do think it could be made to operate under higher frequencies, the issue why I never changed that myself is that the interface IC uses the same code (I think), and since it has the same baudrate error it works up to high frequencies.
posted by Erik - 09 Nov 2014Should we look at the latest cmsis files for freescale and test those if they work? I can paste them and share a link. Paul, what do you think?
posted by Martin Kojtal 09 Nov 2014That may be a good idea Martin. I did dig a little deeper with this and found that I could get the connection working at 256k if I set my display to a strange value of 282353 Baud that this display has. But that was only on one of my boards where I have another clock set up to enable the KL25Z at 32Khz crystal mode (non Mbed standard). I then tried another board with the same crystal set up and same code and this did not work. I checked the 32Kz frequency and there were some differences that may account for this. However I do believe the preescalers may be set incorrectly so at higher rates the error is too great to synchronise the data flow.
But the question is can the serial preescalers be changed without impacting other parts (i2c, SPI, etc). If this is the case the only way round this problem would be to set an offset to the baud rate to match the display.
Erik, I don't think the user program baud rate would impact on the SDA MCU, but perhaps the pc.serial print function would have issues (KL25Z). I may try the pc.serial print at 256k baud (if that is possible) and see if get similar results.
posted by Paul Staron 11 Nov 2014