1 Reply Latest reply on Jan 5, 2020 11:49 PM by ChunleiL_51

    CYBT 343026


      1.根据模块的data sheet 模块应该有24MHZ 的晶振和128KHZ 的晶振是吗?
      2. TIME WAKE 模式时设备的RTC time 用的是内部128 KHZ 的晶振是吗?

      3.当设备起来唤醒跑的时候RTC 的时间 用的是24MHZ 的晶振吗?还是 一直用128khz 的晶振作为RTC 的时间源?

      4切换主频使用wiced_bool_t wiced_update_cpu_clockz()这个函数是吧?

        • 1. Re: CYBT 343026



          1. 根据相关文档,CYBT-343026-01应该只在CYW20706芯片外使用了一个24MHz的晶振,作为XTAL来源。模组内置的芯片CYW20706只要求一个XTAL,并且如模组的DataSheet所述,模组在设计时也只提供了一个24MHz主晶振。
          2. RTC可使用外部的XTAL32K晶振源(External LPO clock)或内部的LPO晶振源,但频率应都是32.768kHz的。
          3. 参照第2点回答。具体使用哪个,电源管理模块(PMU)会根据精度要求等自行管理,并无固定搭配。
          4. 切换主频使用的是wiced_bool_t wiced_update_cpu_clock(),题主您的函数名最后多了一个'z'

          展开描述一下:对于WICED系列的CYBT芯片,其多由CYW20xxx系列芯片驱动,该系列芯片在设计时需要提供一个24MHz的主晶振(main crystal oscillator),并推荐提供一个高精度的32kHz的晶振作为可选的External LPO clock (XTAL32K)。其他的时钟和晶振源都是在此之上产生。


          LPO是Low-Power Oscillator,根据文档所述,LPO有以下三种来源:

          The LPO is a clock that runs in low-power modes to source some blocks. This clock is used to time the wakeup at desired intervals. This clock has low power consumption, which makes it ideal for operation in low-power modes. The Bluetooth specification requires an accuracy of ±250 ppm for Basic Rate/Enhanced Data Rate (BR/EDR) and ±500 ppm for Bluetooth Low Energy (BLE). Therefore, the LPO accuracy must lie within this range if there is an active Bluetooth operation. The LPO uses one of the following possible sources:

          • Low Power Xtal (LPX): This clock is derived from the external main crystal oscillator but runs in low-power mode during sleep. LPX typically has a frequency of 1 MHz, which is derived from the 24-MHz crystal and provides a clock accuracy of 20 ppm or better but consumes relatively more current compared to other LPO sources. LPX is useful when maintaining a BR/EDR connection in a master role where high accuracy is required. It can sometimes also serve as a substitute for the external 32-kHz crystal.
          • External LPO clock: CYW208xx has pins to which an external digital clock or a 32.768-kHz crystal can be connected. The accuracy should be within ±250 ppm as required by the Bluetooth specification. If an external LPO is used, then the PMU will use this under all conditions when a 20-ppm clock is not required. If a 20-ppm clock is required at any time, then the LPX will be used instead of the external LPO clock.
          • Internal LPOs: The internal LPOs belong to the Lean High Land (LHL) domain, which is always powered ON. There are two internal LPOs: one which has lower accuracy and consumes less current, and another with higher accuracy but consumes more current. These LPOs are calibrated by the PMU and used based on the accuracy required by the BT subsystem.



          特别是这篇文档(CYW20819 Feature and Peripheral Guide),其虽不是CYW20706的Guide手册,但其5.3-5.6章节系统地描述了该系列的系统时钟相关的资源设计,这里贴出截图供参考:






          Best Regards

          C. L.