STM32WBA65 PDM2PCM and BLE share CRC

[JFisher-Legato]

Hello,

I am looking for guidance on how to share the CRC peripheral between two modules. For instance, in our application we are using the BLE stack (for example, following this: https://wiki.st.com/stm32mcu/wiki/Connectivity:STM32WBA_BLE_STM32CubeMX#STM32CubeMX_initial_setup). We also are using the SAI interface to sample PDM microphones, and using the PDM2PCM middleware. The PDM2PCM library has something of a hidden dependency on the CRC being enabled.

My question is - will the two modules conflict? I notice that in app_entry.c there is a mutex being used to control access to the CRC interface (presumably).

How should I ensure that the two requirements don't clash with each other?

Thank you,
Jonathan

[TMANE.1]

Hello, 

The PDM2PCM library uses the CRC during PDM_Filter_Init() only and bypasses the crc_ctrl.c. At this time the PDM2PCM requires the CRC to be configured with default values (CRC_CR = 0x000000000 and CRC_POL = 0x04C11DB7).

The STM32WBA BLE Framework uses the CRC with a configuration different from the default (for the NVM). 

A possibility would be to add a config in the crc_ctrl_conf.c :

CRCCTRL_Handle_t PDM2PCM_Handle =
{
  .Uid = 0x00,
  .PreviousComputedValue = 0x00,
  .State = HANDLE_NOT_REG,
  .Configuration =
  {
    .DefaultPolynomialUse = DEFAULT_POLYNOMIAL_ENABLE,
    .DefaultInitValueUse = DEFAULT_INIT_VALUE_ENABLE,
  },
};

Then register the handle with CRCCTRL_RegisterHandle(&PDM2PCM_Handle); and call CRCCTRL_Calculate(&PDM2PCM_Handle, ...) just before PDM_Filter_Init() with some void parameters to force the CRC reconfiguration. (You must ensure the CRC is not used between these two calls....)

Otherwise, you can do yourself the CRC reconfiguration / restoration around PDM_Filter_Init(). In that case, note the CRC_CR RESET does not reset all registers such CRC_POL. 

Best regards,