Interfacing ESP32 to MCU via SPI

[Swathi B K]

Hello everyone,
I am working on interfacing MCU with esp32 via SPI. I am very much new to esp32 and i did not get enough reference for interfacing esp32 with other MCU. Can anyone guide me, how to interface and what are the prerequisite i should have?
Attempted:
1. I tried interfacing two ESP32 WROOM 32 via SPI using ESP IDF and i used SPI SLAVE DRIVER example code. I was able to interface and i found it working.
2. I tried with one ESP32 and one MCU where i flashed SPI receiver example to ESP32 and initialized SPI in MCU as master. I was able to verify that data from MCU is available on SDO line of MCU but i am not getting any kind of response from ESP32.

Kindly, guide me the procedure to interface MCU with esp32.

Thanks & Regards
Swathi