AM3356: PWM library usage

Hi, 

I am trying to utilize the epwm.h for my PWM implementation. I came across this comment in the epwm_app.c file , can you please elaborate what it means? 

/* ========================================================================== */
/*                                Macros                                      */
/* ========================================================================== */

/* TODO: This macro is not needed. This value should be provided by PRCM info. */
/** \brief Functional clock to the PWMSS. */
#define SOC_EHRPWM_2_MODULE_FREQ      (100U * FREQ_MHZ)

This is in reference to this line of code in the function EPWMAppInit() in the same source file:

/* Get the functional clock value of PWMSS */
            /* TODO: This value has to be provided by the PRCM data base */
            pPwm->funcClk = SOC_EHRPWM_2_MODULE_FREQ;

Does that mean I need to use this API  shown below: 

/**
 * \brief This API gets the input functional clock rate of a module. This can
 *        be used by the device driver API's to get the input clock and configure
 *        the internal multipliers/dividers accordingly. Clock manipulations
 *        inside the module are not modelled here, and left to the individual
 *        module drivers to handle.
 *
 * \param moduleId       Unique ID of the module
 *                           #chipdbModuleID_t
 * \param instNum        Instance number of the module
 * \param clockId        Clock ID of the clock edge to be traversed. For 
 *                       modules like CPSW, DSS etc, where more than one clock 
 *                       feeds the module, one of the clock need to be selected.
 *                           #prcmClockId_t
 * \param *pClockRate    Pointer to get the clock rate in KHz 
 *
 * \retval S_PASS              Clock rate returned in 'clockRate' is valid
 * \retval E_INVALID_PARAM     Invalid module id
 * \retval E_INVALID_OPERATION API called when the module is disabled
 **/
int32_t PRCMGetClockRate(chipdbModuleID_t moduleId, 
                         uint32_t instNum,
                         prcmClockId_t clockId, 
                         uint32_t *pClockRate);

If so, is this the correct parameters I am passing for PWM instance 1 and getting the clock value in "read_var"

What would be the third parameter here for PWM instance 1? I couldn't find the appropriate one for pwm in this structure(in file hw_prcm.h):

/** 
 * \brief Clocks
 */
typedef enum 
{
    PRCM_CLK_L4_CEFUSE_GCLK,
    PRCM_CLK_MIN = PRCM_CLK_L4_CEFUSE_GCLK,
    /*!< Lower bound (inclusive) */
    PRCM_CLK_CUST_EFUSE_SYSCLK,
    PRCM_CLK_DEBUG_CLKA_GCLK,
    PRCM_CLK_DEBUG_CLKB_GCLK,
    PRCM_CLK_DEBUG_CLKC_GCLK,
    PRCM_CLK_L3_AON_GCLK,
    PRCM_CLK_DBGSYSCLK,
    PRCM_CLK_DSS_GCLK,
    PRCM_CLK_DSS_L3_GCLK,
    PRCM_CLK_DSS_L4_GCLK_EN,
    PRCM_CLK_DSS_SYSCLK,
    PRCM_CLK_L4LS_GCLK,
    PRCM_CLK_EMIF_PHY_GCLK,
    PRCM_CLK_DDR_DLL_GCLK,
    PRCM_CLK_DLL_AGING_GCLK,
    PRCM_CLK_EMIF_L3_GICLK,
    PRCM_CLK_L3S_GCLK,
    PRCM_CLK_MMC_FCLK,
    PRCM_CLK_L3_GCLK,
    PRCM_CLK_GFX_GFCLK,
    PRCM_CLK_GFX_L3_GCLK,
    PRCM_CLK_GPIO_1_GDBCLK,
    PRCM_CLK_GPIO_2_GDBCLK,
    PRCM_CLK_GPIO_3_GDBCLK,
    PRCM_CLK_GPIO_4_GDBCLK,
    PRCM_CLK_GPIO_5_GDBCLK,
    PRCM_CLK_MGC_FGCLK,
    PRCM_CLK_L3D2_GCLK,
    PRCM_CLK_ICSS_IEP_GCLK,
    PRCM_CLK_ICSS_OCP_GCLK,
    PRCM_CLK_ICSS_UART_GCLK,
    PRCM_CLK_LCD_L3_GCLK,
    PRCM_CLK_LCD_L4S_GCLK,
    PRCM_CLK_LCD_GCLK,
    PRCM_CLK_CAN_CLK,
    PRCM_CLK_HDQ1W_GCLK,
    PRCM_CLK_I2C_FCLK,
    PRCM_CLK_MCASP_FCLK,
    PRCM_CLK_SPI_GCLK,
    PRCM_CLK_TIMER10_GCLK,
    PRCM_CLK_TIMER11_GCLK,
    PRCM_CLK_TIMER2_GCLK,
    PRCM_CLK_TIMER3_GCLK,
    PRCM_CLK_TIMER4_GCLK,
    PRCM_CLK_TIMER5_GCLK,
    PRCM_CLK_TIMER6_GCLK,
    PRCM_CLK_TIMER7_GCLK,
    PRCM_CLK_TIMER8_GCLK,
    PRCM_CLK_TIMER9_GCLK,
    PRCM_CLK_UART_GFCLK,
    PRCM_CLK_CPSW_CPTS_RFT_CLK,
    PRCM_CLK_CPSW_250MHZ_CLK,
    PRCM_CLK_CPSW_5MHZ_CLK,
    PRCM_CLK_CPSW_50MHZ_CLK,
    PRCM_CLK_CPSW_125MHZ_GCLK,
    PRCM_CLK_MPU_CLK,
    PRCM_CLK_OCPWP_L3_GCLK,
    PRCM_CLK_OCPWP_L4_GCLK_EN,
    PRCM_CLK_RTC_32KCLK,
    PRCM_CLK_L4_RTC_GCLK,
    PRCM_CLK_L4_WKUP_GCLK,
    PRCM_CLK_SR_SYSCLK,
    PRCM_CLK_USBPHY_32KHZ_GCLK,
    PRCM_CLK_WDT0_GCLK,
    PRCM_CLK_WDT1_GCLK,
    PRCM_CLK_TAMPER_L4_GCLK,
    PRCM_CLK_USB_OTG_SS_REFCLK,
    PRCM_CLK_USB_PLL_CLK,
    PRCM_CLK_USIM0_FCLK,
    PRCM_CLK_USIM0_FCLK32,
    PRCM_CLK_USIM1_FCLK,
    PRCM_CLK_USIM1_FCLK32,
    PRCM_CLK_L3S_TSC_GCLK,
    PRCM_CLK_ADC_FCLK,
    PRCM_CLK_24MHZ,
    PRCM_CLK_GPIO0_GDBCLK,
    PRCM_CLK_I2C0_GFCLK,
    PRCM_CLK_L4_WKUP_AON_GCLK,
    PRCM_CLK_SYNCTIMER32K_GFCLK,
    PRCM_CLK_TIMER0_GCLK,
    PRCM_CLK_TIMER1_GCLK,
    PRCM_CLK_UART0_GFCLK,
    PRCM_CLK_STD_EFUSE_SYSCLK,
    PRCM_CLK_MAX = PRCM_CLK_STD_EFUSE_SYSCLK,
    /*!< Enum Upper bound */
    PRCM_CLK_UNDEF = (UINT32_MAX),
    /*!< Undefined value */

} prcmClockId_t;

PRCMGetClockRate(CHIPDB_MOD_ID_PWMSS, 1, ?, read_var);

I look forward to hearing from you.

Thank you,

Arshiya Tabassum

Hi Frank,

Thank you for your detailed explanation.  I appreciate it!

1. I have a follow up question regarding the macro "PRCM_CLK_L4LS_GCLK " . This is defined in for am43xx , I couldn't find anything with the same name under starterware/includes/am335x path. 

Am not sure if I need to use this for am335x, can you please verify? 

2. Even if I assume this is right, and include the path of this hw_prcm.h (shown in the screenshot above) file, I am losing my prcm.h files and getting an error that PRCMGetClockRate() is undefined. Please let me know how to go about this.

3. Lastly, can I use the compile time macro " #define SOC_EHRPWM_2_MODULE_FREQ      (100U * FREQ_MHZ)" to test my pwm in case I won't be able to use the function "PRCMGetClockRate()"? 

Awaiting your response!

Thank you!

Hi  Frank,

Thank you for the update. I was able to make the PWM work and move the motor from the PWM pulses.

I have a question for you related to generating interrupts on PWM. I couln't find an example of epwm interrupt in the rtos package.

I want to achieve the following: 

Count the number of steps my motor has moved by counting the number of pulses of PWM. 

How I am planning to acheive this uisng the epwm library (epwm.h file) is as follows(Q represent questions):

 Enable the Event trigger submodule by selecting the event source and period.

Q.1. What would be my event and period if I want to count the number of pulses ?

When the interrupt is generated, i want to go to the callback function and in that callback I want to keep a count of pulses.

Q.2. How do I link the interrupt generation with my callback function?

Q.3. Can I use the function EPWMEtIntrTrigger() to generate the interrupt on the event source and period that I have configured using the API EPWMEtIntrCfg(baseAddr, pPwm->etCfg.intrEvtSource, pPwm->etCfg.intrPrd);?

Q.4. What are the steps to stop PWM pulses on EHRPWM1A or EHRPWM2A outputs? Just calling EPWMClockDisable() is enough?

Thank you,

Arshiya Tabassum

Hi Frank,

I closed the DMTimer thread and asking the ePWM question here as suggested. 

Thank you for your response and providing the detailed breakdown of timer API usage. I appreciate it!

The only reason I was following the starterware example of DMTimer was because I wanted to see how to use the Interrupt Controller (AINTC) for generating interrupts for ePWM.

Can you please if possible explain, how to generate interrupts on ePWM ?

So far, I have followed the steps as below as directed in AM335x TRM section 15.2.2.2 

1. Disable global interrupts - INTCDisableIntr()

2. Disable ePWM interrupts - EPWMEtIntrDisable()

3. Initialize peripheral registers - Followed ePWM example and initialized all necessary registers

4. Clear any spurious ePWM flags - EPWMEtIntrClear()

5. Enable ePWM interrupts - EPWMEtIntrEnable()

6. Enable global interrupts - INTCEnableIntr()

And, last but not the least, I have enabled the Event Trigger module of ePWM and configured the source as TBCNT=TBPRD event.

I am using the API EPWMEtIntrStatus() to check the status and see that no interrupt is generated. 

Please guide me to see what else I am missing to successfully generate interrupt on my ePWM. 

Looking forward to your response.

Thank you,

Arshiya Tabassum

Hi Arshiya,

For an RTOS application, you shouldn't use the Starterware INTC functions for configuring the Interrupt Controller.

Please see <PDK>\packages\ti\starterware\examples\dcan\readme.txt:

Configuring Interrupts
-----------------------
Major difference for running the StarterWare examples in the baremetal and RTOS environment is the way
interrupts are configured and dispatched. StarterWare baremetal examples configure the interrupts
using INTC and GIC modules. This need to be updated to use the RTOS APIs to add support for TI RTOS.
TI OSAL library should be used to configure the interrupts. All the functions doing the interrupt
configuration shall be updated to use OSAL library APIs.

I suggest trying either of the following:

#1: Use OSAL HWI API in <PDK>\packages\ti\osal\HwiP.h.
Use API functions HwiP_Params_init(), HwiP_create() & HwiP_enableInterrupt().

#2: Use SYS/BIOS HWI, see <BIOS>/docs/cdoc/ti/sysbios/hal/Hwi.html
Use API functions Hwi_Params_init() & HWI_create (or Hwi_construct()) and Hwi_enableInterrupt().

For either approach, the interrupt number should be set to the interrupt number for the ePWM instance listed in TRM, Table 6-1. ARM Cortex-A8 Interrupts.

Otherwise your approach looks good. I would confirm:

• the ePWM counter is running by inspecting TBCNT
• the ePWM interrupt is enabled by inspecting ETSEL

Let me know how it goes..

Regards,
Frank