Exceptions and Interrupts Control
119
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
System Control and Interrupts
1.5.6.1.1 Clock Fail Condition
A main oscillator verification circuit is provided to generate an error condition if the oscillator is running too
fast or too slow or goes missing. This logic is referred to as missing clock detection logic. When a missing
clock error is generated, the CLOCKFAIL bit (bit 1) of the CNMIFLG register is set, the clock source is
switched to the 10 MHz internal oscillator, and the PLL is bypassed.
The CLOCKFAIL NMI is triggered to both the master and control subsystems. Since this NMI is enabled
by default on power up, it is necessary for boot ROM to handle it. Refer to the
Boot ROM
chapter of this
document for more details on how C-Boot ROM handles this NMI.
1.5.6.1.2 ACIBERR NMI
An NMI is generated to both the master subsystem and control subsystem when the error condition in the
ACIB occurs. The ACIBERR bit in the CNMIFLG register is set, and to clear this NMI, the user has to
clear the ACIBERR bit in the CNMIFLG register.
This NMI is disabled by default on reset, and the user can enable this error to trigger an NMI to the C28x
CPU by setting the ACIBERRE bit in the CNMICFG register.
1.5.6.1.3 RAMUNCERR NMI
For information on the RAM Uncorrectable Error NMI, please refer to the
Internal Memory
chapter for
more details. This NMI is generated when a double bit error is detected by the memory wrapper logic.
1.5.6.1.4 FLUNCERR NMI
For information on the FLASH Uncorrectable Error NMI, please refer to the
Internal Memory
chapter for
more details.
1.5.6.2
Control Subsystem NMIWD (CNMIWD) Module
The control subsystem is equipped with an NMI Watchdog module that when a non-maskable interrupt is
triggered, allocates time for the user software to handle the NMI by clearing the error conditions and
clearing the respective flags in the CNMIFLG register or by acknowledging the NMI and gracefully shutting
down the system. If none of the actions mentioned are taken, the CNMIWD counter keeps counting. As
soon as the counter value reaches the CNMIWD period register value, it will generate a CNMIWD reset,
which will reset the entire device.
The CNMIWD counter is clocked by the C28 system clock. The CNMI WatchDog Period register
(CNMIWDPRD) can be programmed with a period limit as per user requirements with the clock cycle limit
the user requires for software to handle or acknowledge the NMI.
1.5.6.2.1 Emulation Considerations
The CNMI watchdog module behaves as below under various debug conditions.
CPU Suspended
When the CPU is suspended, the NMI watchdog counter will be
suspended.
Run-Free Mode
When the CPU is placed in run-free mode, the NMI watchdog counter will
resume operation as normal.
Real-Time Single-Step Mode When the CPU is in real-time single-step mode, the NMI watchdog
counter will be suspended. The counter remains suspended even within
real-time interrupts.
Real-Time Run-Free Mode
When the CPU is in real-time run-free mode, the NMI watchdog counter
operates as normal.