Excessive interrupts in serial port example

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#6 Excessive interrupts in serial port example

Status: open

Owner: Bertrik Sikken

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Priority: 5

Updated: 2007-02-03

Created: 2007-01-14

Creator: Bertrik Sikken

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Some cases of excessive interrupts have been reported, see this thread on the lpcusb forum
https://sourceforge.net/forum/message.php?msg_id=4095179
and this thread on the lpc2000 mailing list
http://tech.groups.yahoo.com/group/lpc2000/message/21597

Discussion

Bertrik Sikken - 2007-02-03

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Bertrik Sikken - 2007-02-03

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The cause of the excessive interrupts seems to be the rate at which the host sends IN tokens. This results in an endless stream of bulk-in NAK interrupts.

A fix that seems to work fine so far:
* BULK IN interrupt handler disables the interrupt-on-NAK feature when the transmit FIFO is empty
* FRAME interrupt handler enables the interrupt-on-NAK feature again when it discovers that there is some data in the transmit FIFO.

Probably a better fix is to enable/disable the bulk-in interrupt, but I can't make that work for currently unknown reason. No more interrupts are seen if the bulk-in interrupt is enabled again.

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Bertrik Sikken - 2007-02-05

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A simple fix has been implemented in revision 142 of the SVN archive: interrupt-on-NAK feature is disabled when sending last packet to host and re-enabled in the USB frame interrupt.

The USB mass storage application example also seems to suffer from the same problem.

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