How to interact to LMP of HC-05 bluetooth module?

Question

Kindly help to enlighten me about the following queries. Thanks in advance.

1. Is HC-05 module a Bluetooth controller?

2. If it is a controller, can we write a host stack for it?

3. Can it replace any Bluetooth chip (e.g WCN Bluetooth chip of snapdragon by Qualcomm) in an android phone?

   in other words, can we interface this module with the android fluoride BT Stack?

4. Can it replace any Bluetooth chip (e.g WCN Bluetooth chip of snapdragon by Qualcomm) in an android phone?

   in other words, can we interface this module with Qcom BT stack or android fluoride BT Stack?

   Note: Of course, it is not comparable with Qualcomm BT chip functionality and performance-wise, but still can we send some basic commands (e.g Inquiry command) to this controller through the fluoride BT stack?

5. Can we directly communicate with the LMP of HC-05 module? And if yes, what is the way to send LMP commands to the HC-05 controller?

6. Can I modify the firmware of HC-05?

I tried to find the answers on internet but I found no satisfactory answers.

Answer 1

Is HC-05 module a Bluetooth controller?

Yes, it is. It uses CSR-BC417 chip (https://cdn.sparkfun.com/datasheets/Wireless/Bluetooth/CSR-BC417-datasheet.pdf) Diagram (https://www.researchgate.net/figure/Pin-Diagram-of-HC-05-Module_fig2_318283686)

If it is a controller, can we write a host stack for it?

Yes, why not (refer to PDF above)

Can it replace any Bluetooth chip (e.g WCN Bluetooth chip of snapdragon by Qualcomm) in an android phone?

Yes and no. As it implemets standard Bluetooth HCI interface it can be done but any way you need driver.

in other words, can we interface this module with the android fluoride BT Stack?

Probably yes, but I'm not very familiar with Android. And may require custom firmware

Can it replace any Bluetooth chip (e.g WCN Bluetooth chip of snapdragon by Qualcomm) in an android phone? in other words, can we interface this module with Qcom BT stack or android fluoride BT Stack?

Probably yes. Depends on how it is implemente don Android.

Can we directly communicate with the LMP of HC-05 module? And if yes, what is the way to send LMP commands to the HC-05 controller?

Yes, as based on PDF above it supports HCI interface.

Can I modify the firmware of HC-05?

Yes as it allows to upload firmware nothing prevents from upload custom one.

Just simple googling with "HC-05 chip" and "HC-05 schematic"gives all the answers.

Edited: Here is more information about CSR chips programming: https://github.com/lorf/csr-spi-ftdi