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Old 12-07-2007, 03:17 AM   #1
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Lightbulb Why the 'N_TTY_BUF_SIZE' is restricted as 4096?

Hi All,

I have one doubt in linux kernel. I.e. Why the 'N_TTY_BUF_SIZE' is defined as 4096 in 'tty.h' file. I have checked linux kernels from 2.6.10 to 2.6.23 in all these sources the tty buffer size value is defined as 4096. Due to this i couldnt able to read more than 4096 bytes from a serial device which is connected in 'ttyUSB0' using a single read operation. but when i increased the value 'N_TTY_BUF_SIZE' in tty.h file it reads characters upto increased values.

If any one knows the reason for restricting the 'N_TTY_BUF_SIZE' to 4096pls share the same.

Old 12-07-2007, 10:05 PM   #2
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I can't answer your question, but fail to see how this (can't
read more than 4096 bytes in one operation) is a problem. There
has to be some arbitrary value, and I *guess* that 4096 may be
something to do with the block-size for LZW compression.

Old 12-10-2007, 03:36 AM   #3
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Thanks for your response!!!

what i am saying is as of now with a single read operation i can read only 4096 bytes from the device. To read more than 4096 bytes i have to use multiple read operations. using this also i couldnt able to read more than 5500 bytes.

so i have increased the value of 'N_TTY_BUF_SIZE'.
please say whether this change will cause any performance degradation. If so what is the optimal solution for reading large no of data from the device.



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