Reset Control
91
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
System Control and Interrupts
1.3.2.1.4 Watchdog Timers Reset Cause (WDT0, WDT1, MNMIWD)
Watchdog Timer 0, Watchdog Timer 1, and the Master NMI WD timer resets will cause a low pulse on
XRS, which will reset the entire device. These resets are handled the same way as an XRS reset. Note
that M-Boot ROM only clears the XRS bit (bit 0 in the MRESC register). It will not clear any other bits in
the MRESC register to allow the user application to handle the actual reset cause if it occurred because of
any WD timers.
1.3.2.1.5 Master Software Reset Cause
For a software reset cause, M-Boot ROM will zero initialize the stack memory for boot ROM execution and
continues to boot. Clock settings are not changed by boot ROM for this reset cause.
1.3.2.1.6 Master Debugger Reset Cause
The master subsystem, the control subsystem, and shared resources are reset for this reset type. If M-
BootROM is executed after this reset, the clock settings are not changed.
1.3.2.2
Control Subsystem Reset Handling
The C28x CPU is reset by the C28RSTIN signal and the C28x CPU, in turn, resets the rest of the control
subsystem with the C28SYSRST signal.
The C28RSTIN signal has five possible sources: XRS, C28NMIWD, M3SWRST, M3DBGRST, and
M3RSNIN. The C28NMIWD is set in response to time-out conditions of the C28x NMI Watchdog. The
M3SWRST is a software-generated reset output by the NVIC. The M3DBGRS is a debugger-generated
reset that is also output by the NVIC. The M3RSNIN reset comes from the Cortex-M3 subsystem to
selectively reset the control subsystem from Cortex-M3 software. The C28x processor can learn the status
of the internal ACIBRST reset signal and the external XRS pin by reading the DEVICECNF register.
As shown in
, for the POR, XRS, MWDT0, MWDT1, and MNMIWD resets, both the master and
control subsystems are reset and the control subsystem is held in reset. Also, M-Boot ROM will bring the
control subsystem out of reset and it will start executing code in its ROM when out of reset.
Master software and master debugger resets propagate to the control subsystem. The control subsystem
will not be held in reset. Instead, it will restart executing software in the control subsystem boot ROM.
Note:
For the control subsystem to see the master software and debugger resets, it should be in the RUN
state. If the control subsystem is under DEBUG HALT and the master subsystem sends a debugger reset,
the control subsystem will miss this reset.
The control subsystem core and control subsystem peripherals are only reset by the C28 (control
subsystem) debugger and NMIWD resets. When the control subsystem is reset by CNMIWD reset, it will
reset and restart running software code in the control subsystem ROM. In addition, an NMI is generated to
the master subsystem indicating that the control subsystem is reset by an NMI. If the master subsystem
does not handle or acknowledge this NMI, the master subsystem is also reset, and a bit is set in the
MRESC register which tells which C28NMI was unserviced that caused a reset.
Unlike the master subsystem which has a reset cause register, the control subsystem does not.