Also I want to know how to make a delay in qemu.
For example, when I send a UART data, there is a certain time interval from setting the register to when the data is sent. Most of this time does not affect the simulation effect, but some guest firmware will execute errors when there is no such delay. This is a comparison. Few, but it does exist.
My question is, if I really want to add such a delay, how to do it. For example, in USART, can I set a callback for sending completion, or add some delays that will not cause qemu to freeze.