Use configuration CDCACM_DISABLE_TXBUF or CDCACM_DISABLE_RXBUF to choose
whether to use usb req buffer as the serial buffer. Since the default
value is n (not using req buf), the original configuration of buf is valid.
This reverts commit 21c8ed80bd.
- migrated /README are removed from /boards
- there are a lot of READMEs that should be further converted to rst.
At the moment they are moved to Documentation/platforms and included in rst files
