Intel IXC1100, IXP42X Debugger Actions, Debug Handler Actions

Intel® IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 123
Intel XScale® Processor—Intel® IXP42X product line and IXC1100 control plane processors
3.6.14.5 Dynamically Loading IC After Reset
An external host can load code into the instruction cache “on the fly” or “dynamically.”
This occurs when the host downloads code while the processor is not being reset.
However, this requires strict synchronization between the code running on the IXP42X
product line and IXC1100 control plane processors and the external host. The
guidelines for downloading code during program execution must be followed to ensure
proper operation of the processor. The description in this section focuses on using a
debug handler running on the IXP42X product line and IXC1100 control plane
processors to synchronize with the external host, but the details apply for any
application that is running while code is dynamically downloaded.
To dynamically download code during software debug, there must be a minimal debug
handler stub, responsible for doing the handshaking with the host, resident in the
instruction cache. This debug handler stub should be downloaded into the instruction
cache during processor reset using the method described in “Loading IC During Reset”
on page 119. “Dynamic Code Download Synchronization” on page 124 describes the
details for implementing the handshaking in the debug handler.
Figure 28 shows a high level view of the actions taken by the host and debug handler
during dynamic code download.
The following steps describe the details for downloading code:
• Since the debug handler is responsible for synchronization during the code
download, the handler must be executing before the host can begin the download.
The debug handler execution starts when the application running on the IXP42X
product line and IXC1100 control plane processors generate a debug exception or
when the host generates an external debug break.
• While the DBGTX JTAG instruction is in the JTAG IR (see “DBGTX JTAG Command”
on page 105), the host polls DBG_SR[0], waiting for the debug handler to set it.
• When the debug handler gets to the point where it is OK to begin the code
download, it writes to TX, which automatically sets DBG_SR[0]. This signals the
host it is OK to begin the download. The debug handler then begins polling
TXRXCTRL[31] waiting for the host to clear it through the DBGRX JTAG register (to
indicate the download is complete).
• The host writes LDIC to the JTAG IR, and downloads the code. For each line
downloaded, the host must invalidate the target line before downloading code to
Figure 28. Downloading Code in IC During Program Execution
DBGRX
JTAG IR DBGTX LDIC
wait for handler to signal download code
signal handler
Handler begins execution signal host ready wait for host to signal
download is complete
continue execution.
ready to start download
for download download complete
Debugger Actions
Debug Handler Actions
clock
15 TCKs