Not reading, or sending, fast enough on my serial application

Hello,

Thanks to those who responded earlier this week to my posting about
needing help with my serial programming. I'm past that hurdle (the
hurdle I was trying to clear ended up being one of my own "genius"),
but now I'm seeing that my application drops packets.

Now, I'm trying isolate where I'm having difficulty. The code places
the serial driver in raw, non-canonical, mode for all the read and
write calls. So I have two questions.

Pertinent information: packet size is 255 bytes.

1) on the send, or write, side of the app. I simply open the serial
line and write the 2500 packets to it. This part of the application
takes, approx., 5 seconds to complete. I'm wondering, since the serial
line is set to 115200 BAUD, am I'm writing the data to the device
faster than the kernel can send it and therefore bits are being dropped
in the buffer before being sent?

2) on the receive, read, side; I again place the serial line in raw
mode and then set the c_cc[VMIN] member to the packet size and then set
the c_cc[VTIME] member to 0. I also call fcntl to set the FNDELAY flag
on the descriptor and then use select() with a timeout of 30 seconds on
the file descriptor (the extremely long timeout is only to allow the
user to start the sender on another computer before the timeout). What
I'm wondering is, am I incorrectly using these facilities? Since I'm
setting VMIN to 255, is select extraneous? Also, since I'm setting
VMIN to 255 AND I'm setting the flags to FNDELAY, is the read still
being blocked until the 255 characters are present?


Andy

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