On 30. 11. 20, 22:22, Mychaela Falconia wrote:
2) For situations in which the luxury of a custom USB ID is not available, e.g., a situation where the device that does not tolerate automatic DTR/RTS assertion on open is a physical RS-232 device that can be connected to "any" serial port, the new sysfs attribute comes to the rescue. Johan's patch comments say that the new flag can also be brought out to termios in the future, similarly to HUPCL,
The difference to other control flags is that open raises DTR/RTS in any case (i.e. including O_NONBLOCK) -- provided baud rate is set (and it is for casual serials). That means you cannot open a port to configure it (using e.g. setserial) without actually raising the DTR/RTS.
but I question the usefulness of doing so, as it is a chicken and egg problem: one needs to open the tty device in order to do termios ioctls on it, and if that initial open triggers DTR/RTS hardware actions, then the end user is still screwed. If Johan or someone else can see a potential use case for manipulating this new flag via termios (as opposed to sysfs or USB-ID-based driver quirks), perhaps you could elaborate on it?
We would need to (ab)use another open flag (e.g. O_DIRECT). I am not biased to either of solutions.
thanks, -- js
