ARM DS-5 Using the Debug Hardware Configuration Utilities

Configuring debug hardware for GDB9.17 DCC and interruptsThe use of DCC interrupts has significant speed implications when using Virtual Ethernet/TTYmode. If possible, you must tie DCC interrupts into the interrupt system of the target and be ableto enable and disable the read and write interrupt individually.NoteThis is a configuration item that you must select when configuring the kernel, when using anARM driver.debug hardware uses JTAG to control debug operations, and JTAG is used to send and receivedata over DCC. debug hardware polls the target JTAG for status:• If interrupts are used, the target is interrupted when data is written to the DCC register orread from it. This enables the target to deal quickly with the data, and continue normalprocessing.• If interrupts are not available, the target must regularly poll the DCC register for any newdata. This means that the target wastes time checking the register for data when none ispresent. Subsequent data is only discovered at the next poll.If debug hardware finds that there is data to be transferred into or out of DCC, it attempts totransfer as many words as possible in one burst, up to a predefined limit. However, if the targethas not sent more data or emptied its transfer register, debug hardware breaks out of its burstand begins polling the execution status and DCC.9.17.1 See alsoTasks• Connecting to targets from GDB through debug hardware on page 9-22• Setting DCC parameters on page 9-23.Reference• Debug hardware TCP/IP port numbering on page 9-6• DCC modes on page 9-7.ARM DUI 0498F Copyright © 2010-2012 ARM. All rights reserved. 9-25ID021112Non-Confidential