1.3.2.7 NMI Interrupt and Watchdog
The NMI watchdog (NMIWD) is used to detect and aid in recovery from a clock failure condition. The NMI
interrupt enables the monitoring of a clock failure. In 280x/2833x/2823x devices, when the VCOCLK counter
overflows (due to loss of input clock), a missing clock condition is detected and a missing-clock-reset (MCLKRS)
is generated immediately. In this device, a CLOCKFAIL signal is generated first, which is then applied to the NMI
watchdog circuit and a reset can be generated after a preprogrammed delay. Alternatively, an interrupt can be
asserted. This feature is not enabled upon power-up, however. That is, when this device first powers up, the
MCLKRS signal is generated immediately upon a clock failure like on 280x/2833x/2823x devices. The user must
enable the generation of the NMI signal with the CLKCTL[NMIRESETSEL] bit. Note that the NMI watchdog is
different from the watchdog described in
.
When the OSCCLK goes missing, the CLOCKFAIL signal triggers the NMI and gets the NMIWD counter running.
In the NMI ISR, the application is expected to take corrective action (such as gracefully shut down the system
before a reset is generated or clear the CLOCKFAIL and NMIINT flags and switch to an alternate clock source,
if applicable). If this is not done, the NMIWDCTR overflows and generates an NMI reset (NMIRS) after a
preprogrammed number of SYSCLKOUT cycles. NMIRS is fed to MCLKRS to generate a system reset back into
the core. Note that NMI reset is internal to the device and will not be reflected on the XRS pin.
The CLOCKFAIL signal could also be used to activate the TZ5 signal to drive the PWM pins into a high
impedance state. This allows the PWM outputs to b tripped in case of clock failure.
CLOCKFAIL interrupt mechanism. Likewise, TZ6 is connected to EMUSTOP output from the CPU. This allows
the user to configure trip action during a CPU halt, such as during emulation or debug sessions.
NMIFLG[NMINT]
1
0
Generate
Interrupt
Pulse
When
Input = 1
NMINT
Latch
Clear
Set
Clear
NMIFLGCLR[NMINT]
XRS
0
NMICFG[CLOCKFAIL]
Latch
Clear
Set
Clear
XRS
NMIFLG[CLOCKFAIL]
NMI Watchdog
SYSCLKOUT
SYSRS
NMIRS
NMIWDPRD[15:0]
NMIWDCNT[15:0]
NMIFLGCLR[CLOCKFAIL]
SYNC?
NMIFLGFRC[CLOCKFAIL]
SYSCLKOUT
See System
Control Section
CLOCKFAIL
A.
The NMI watchdog module is clocked by SYSCLKOUT. Due to the limp mode function of the PLL, SYSCLKOUT is present even if the
source clock for OSCCLK fails.
Figure 1-35. Clock Fail Interrupt
System Control and Interrupts
88
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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