NXP Semiconductors LPC24XX UM10237 - Manual (Page 751)

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User manual Rev. 04 — 26 August 2009 751 of 792
NXP Semiconductors
UM10237
Chapter 35: LPC24XX RealMonitor
– Undef exception caused by the undefined instructions in user foreground
application. This indicates an error in the application being debugged. RealMonitor
stops the user application until a "Go" packet is received from the host.
When one of these exceptions occur that is not handled by user application, the following
happens:
• RealMonitor enters a loop, polling the DCC. If the DCC read buffer is full, control is
passed to rm_ReceiveData() (RealMonitor internal function). If the DCC write buffer is
free, control is passed to rm_TransmitData() (RealMonitor internal function). If there is
nothing else to do, the function returns to the caller. The ordering of the above
comparisons gives reads from the DCC a higher priority than writes to the
communications link.
• RealMonitor stops the foreground application. Both IRQs and FIQs continue to be
serviced if they were enabled by the application at the time the foreground application
was stopped.
4. How to enable RealMonitor
The following steps must be performed to enable RealMonitor. A code example which
implements all the steps can be found at the end of this section.
4.1 Adding stacks
User must ensure that stacks are set up within application for each of the processor
modes used by RealMonitor. For each mode, RealMonitor requires a fixed number of
words of stack space. User must therefore allow sufficient stack space for both
RealMonitor and application.
RealMonitor has the following stack requirements:
4.2 IRQ mode
A stack for this mode is always required. RealMonitor uses two words on entry to its
interrupt handler. These are freed before nested interrupts are enabled.
4.3 Undef mode
A stack for this mode is always required. RealMonitor uses 12 words while processing an
undefined instruction exception.
4.4 SVC mode
RealMonitor makes no use of this stack.
Table 682. RealMonitor stack requirement
Processor mode RealMonitor Stack Usage (Bytes)
Undef 48
Prefetch Abort 16
Data Abort 16
IRQ 8