[问答]

NUC240如何调整prescaler值?

问答对人有帮助，内容完整，我也想知道答案 0 各位大大安安，我在学习NUC240 BSP中Smpl_Basic01_PWM_Capture范例，输入的PWM频率范围在0~100Hz区间，量测周期结果不是输入的PWM频率，是否该设定PWM_ConfigCaptureChannel中的参数才能正确量测? /** * @brief Configure PWM capture and get the nearest unit time. * @param[in] pwm The pointer of the specified PWM module * @param[in] u32ChannelNum PWM channel number. Valid values are between 0~3 * @param[in] u32UnitTimeNsec The unit time of counter * @param[in] u32CaptureEdge The condition to latch the counter. This parameter is not used * @return The nearest unit time in nano second. * @details This function is used to configure PWM capture and get the nearest unit time. / uint32_t PWM_ConfigCaptureChannel(PWM_T pwm, uint32_t u32ChannelNum, uint32_t u32UnitTimeNsec, uint32_t u32CaptureEdge) { uint32_t u32Src; uint32_t u32PWMClockSrc; uint32_t u32PWMClkTbl[8] = {__HXT, __LXT, NULL, __HIRC, NULL, NULL, NULL, __LIRC}; uint32_t u32NearestUnitTimeNsec; uint8_t u8Divider = 1; /* this table is mapping divider value to register configuration / uint32_t u32PWMDividerToRegTbl[17] = {NULL, 4, 0, NULL, 1, NULL, NULL, NULL, 2, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 3}; uint16_t u16Prescale = 2; uint16_t u16CNR = 0xFFFF; if(pwm == PWMA) { if(u32ChannelNum < 2)/ channel 0 and channel 1 / u32Src = ((CLK->CLKSEL2 (CLK_CLKSEL2_PWM01_S_EXT_Msk)) >> (CLK_CLKSEL2_PWM01_S_EXT_Pos - 2)) \| (CLK->CLKSEL1 (CLK_CLKSEL1_PWM01_S_Msk)) >> (CLK_CLKSEL1_PWM01_S_Pos); else / channel 2 and channel 3 / u32Src = ((CLK->CLKSEL2 (CLK_CLKSEL2_PWM23_S_EXT_Msk)) >> (CLK_CLKSEL2_PWM23_S_EXT_Pos - 2)) \| (CLK->CLKSEL1 (CLK_CLKSEL1_PWM23_S_Msk)) >> (CLK_CLKSEL1_PWM23_S_Pos); } else /pwm == PWMB/ { if(u32ChannelNum < 2)/ channel 0 and channel 1 / u32Src = ((CLK->CLKSEL2 (CLK_CLKSEL2_PWM45_S_EXT_Msk)) >> (CLK_CLKSEL2_PWM45_S_EXT_Pos - 2)) \| (CLK->CLKSEL2 (CLK_CLKSEL2_PWM45_S_Msk)) >> (CLK_CLKSEL2_PWM45_S_Pos); else / channel 2 and channel 3 / u32Src = ((CLK->CLKSEL2 (CLK_CLKSEL2_PWM67_S_EXT_Msk)) >> (CLK_CLKSEL2_PWM67_S_EXT_Pos - 2)) \| (CLK->CLKSEL2 (CLK_CLKSEL2_PWM67_S_Msk)) >> (CLK_CLKSEL2_PWM67_S_Pos); } if(u32Src == 2) { SystemCoreClockUpdate(); u32PWMClockSrc = SystemCoreClock; } else { u32PWMClockSrc = u32PWMClkTbl[u32Src]; } u32PWMClockSrc /= 1000; for(; u16Prescale <= 0x100; u16Prescale++) { u32NearestUnitTimeNsec = (1000000 u16Prescale * u8Divider) / u32PWMClockSrc; if(u32NearestUnitTimeNsec < u32UnitTimeNsec) { if((u16Prescale == 0x100) (u8Divider == 16)) //limit to the maximum unit time(nano second) break; if(u16Prescale == 0x100) { u16Prescale = 2; u8Divider <<= 1; // clk divider could only be 1, 2, 4, 8, 16 continue; } if(!((1000000 * ((u16Prescale * u8Divider) + 1)) > (u32NearestUnitTimeNsec * u32PWMClockSrc))) break; continue; } break; } // Store return value here 'cos we're gonna change u8Divider u16Prescale u16CNR to the real value to fill into register u16Prescale -= 1; // convert to real register value u8Divider = u32PWMDividerToRegTbl[u8Divider]; // every two channels share a prescaler (pwm)->PPR = ((pwm)->PPR ~(PWM_PPR_CP01_Msk << ((u32ChannelNum >> 1) * 8))) \| (u16Prescale << ((u32ChannelNum >> 1) * 8)); (pwm)->CSR = ((pwm)->CSR ~(PWM_CSR_CSR0_Msk << (4 * u32ChannelNum))) \| (u8Divider << (4 * u32ChannelNum)); // set PWM to edge aligned type (pwm)->PCR = ~(PWM_PCR_PWM01TYPE_Msk << (u32ChannelNum >> 1)); (pwm)->PCR \|= PWM_PCR_CH0MOD_Msk << (8 * u32ChannelNum); ((__IO uint32_t )((((uint32_t) ((pwm)->CNR0)) + (u32ChannelNum) * 12))) = u16CNR; return (u32NearestUnitTimeNsec); } 实际输入PWM频率100Hz，量测得到Total Period = 60399，利用下面公式计算频率=12000000/2/60399=99.36Hz假设输入PWM频率为50Hz，(CNR+1)=120000000/2/50=120000 大于65536，所以必须增大prescaler值，请问该如何调整prescaler值? 0
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