I would like to announce limited quantity availability of the FE310-G000! This is the same silicon that powers the SiFive HiFive1 board which can now be used in your own boards and projects. The FE310-G000 is available from Crowd Supply in quantities of 5 for $25 via the link below (same page as the HiFive1 boards):
In the SiFive-FE310-G000-manual-v2p0.pdf, section 19.4:
19.4 Receive Data Register (rxdata)
Reading the rxdata register dequeues a character from the receive FIFO, and returns the value
in the data field. The empty flag indicates if the receive FIFO was empty; when set, the data field
does not contain a valid character. Writes to rxdata are ignored.
There is no empty flag listed in the register description table 19.3 (I’m assuming it is bit 31)