Dear Mike Frysinger,
In message 201204231657.18531.vapier@gentoo.org you wrote:
That's why I wrote "or rather from fd 0".
reading directly from fd 0 makes no difference. stdin is stdin. if stdin is
stdin is stdin (a FILE pointer which uses all the automatic buffering from stdio), and fd 0 is fd 0 (a plain file descriptoor you can use as you like).
backed by a tty, you need to behave differently than if it's backed by a pipe.
This does not play any role in this context, or does it?
That's why I suggested to use select() or poll() to poll for available characters, just like the hardware does. Only we do NOT want to tun this in a tight loop. We will most likely want to add a sufficiently large delay to keep CPU load in reasonable bounds.
where exactly do you propose adding this delay ? tstc() is called in many places (not just the main console loop), many of which are done simply to handle the unlikely CTRL+C interrupt. thus we don't want tstc() delaying at all or it'll slow down random CPU-bound operations.
It makes _zero_ sense to burn 100% CPU with this code. Adding a few 10 ... a few 100 us delay tstc() will probably not be noticed.
Did you try that out?
also, what you're proposing is changing the behavior of u-boot when it's in the sandbox so that it acts less like the hardware. when you run u-boot on the hardware and it's sitting at the prompt, u-boot is running the cpu at 100%.
Correct. But then U-Boot is the only master of the CPU, and nothing else can be run in parallel.
In the sandbox, U-Boot is an ordinary user space application and as such is supposed to behave well. Burning 100% CPU is a polling input loop is about the most stupid thing we can do.
Why invent new methods when we can encapsulate this in the input interface?
i'm not inventing new methods. i'm telling you that the sandbox OS layer today cannot access the C library's errno because u-boot's own implementation of errno is overriding it. so any call sandbox makes to the OS (like read() or select() or poll()) that results in an error, sandbox has no way of knowing the underlying reason.
Than this needs to be fixed for sandbox?
Best regards,
Wolfgang Denk