SPI Mode get change in execution it get stuck

[MDeva.1]

I am working on Nucleo-h745ziq board .I have to board i am doin the loop-backing. One board as master and another as slave. First I configure as both board as full duplex. After switching the switch the mode get change the MASTER only transmit and slave only receive data. But when switch get pressed it get stuck. After switching 4-5 times of switch the garbage data is get. How i can resolve these issue can you help me?

[S.Ma]

Use NSS as start/stop sync event. Use EXTI on the slave NSS gpio to get interrupt and prepare the message to exchange. Use full duplex on both ends. Allow the master a small pause after nss toggles for the slaves to get ready to transfer. This is one way, detail implementation depdends on protocol chosen.