CHAPTER 3 SYSTEM CONTROLLER
224 Preliminary User’s Manual S15543EJ1V0UM
3.6 DSU (Deadman’s SW Unit)
3.6.1 Overview
The DSU detects when the VR4120A is in runaway (endless loop) state and resets the VR4120A. The use of the
DSU to minimize runaway time effectively minimizes data loss that can occur due to software-related runaway states.
3.6.2 DSUCNTR (DSU Control Register)
This register is used to enable use of the Deadman’s Switch functions.
DSUCNTR is a 32-bit word-aligned register. Default is 0H.
Bits Field R/W Default Description
31:1 Reserved R/W 0 Hardwired to 0.
0 DSWEN R/W 0 Deadman’ s Switch function enable
1 = enable
0 = disable
3.6.3 DSUSETR (DSU Time Set Register)
This register sets the Deadman’s Switch cycle. The Deadman’s Switch cycle can be set in 1-clock increments in a
range from 1 to 232 – 1 clock. The DSUCLRR’s DSWCLR bit must be set by means of software within the specified
cycle time. DSUSETR is a 32-bit word-aligned register. Default is 8000_0000H.
Bits Field R/W Default Description
31:0 DEDTIM R/W 8000_
0000H
Deadman’s Switch cycle setting
DSU cycle = DEDTIME value system clock period
(100 MHz:10 ns, 66 MHz:15 ns)
example:
DEDTIM = 05F5_E100H (100 MHz) or 03F9_40AAH (66 MHz)
-> DSU cycle = 1 sec
DEDTIM = 0BEB_C200H (100 MHz) or 07F2_8154H (66 MHz)
-> DSU cycle = 2 sec
DEDTIM = 11E1_A300H (100 MHz) or 0BEB_C200H (66 MHz)
-> DUS cycle = 3 sec
: : :
3.6.4 DSUCLRR (DSU Clear Register)
Setting the DSWCLR bit in this register to ‘1’ clears the Deadman’s Switch counter. The VR4120A is reset
automatically if a ‘1’ is not written to the bit within the period specified in DSUSETR. DSUCLR is a 32-bit word-aligned
register. Default is 0H.
Bits Field R/W Default Description
31:1 Reserved W 0 Hardwired to 0.
0 DSWCLR W 0 Deadman’s Switch counter clear. Cleared to 0 when 1 is written.
1 = Clear
0 = Don’t clear