Got it.

Peter Maydell <peter.maydell@linaro.org> 于2021年9月8日周三 下午5:47写道：

> On Wed, 8 Sept 2021 at 03:50, Duo jia <jiaduo19920301@gmail.com> wrote:
> > 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.
>
> You can do this kind of thing with an additional timer.
> Look at hw/char/cadenc_uart.c and its handling of char_tx_time
> for an example. In that case it is (despite the name)
> modelling slow data receive, not slow data transmit, but
> the basic idea is the same.
>
> As you say, though, very little guest code really cares about
> UART character timings (and the guest code that does is probably
> buggy strictly speaking). So if I were you I would put "model
> delays in UART timings" very low on your priority list...
>
> -- PMM
>