MSC8144E Reference Manual, Rev. 3
21-16
Freescale
Semiconductor
Timers
Although most software disciplines permit or even encourage the watchdog concept, some
systems require a selection of time-out periods. For this reason, the software watchdog timer
must provide a selectable range for the time-out period. Figure 21-6 shows how to handle this
need.
Figure 21-6. Software Watchdog Timer Functional Block Diagram
In Figure 21-6, the range is determined by SWCRR[SWTC]. The value in SWTC is then loaded
into a 16-bit decrementer clocked by the CLASS64 clock. An additional divide-by-65536
prescaler value is used when needed.
The decrementer begins counting when loaded with a value from SWTC. After the timer reaches
0x0, a software watchdog expiration request is issued to the reset or MCP (machine check
processor) control logic. Upon reset, SWTC is set to the maximum value and is again loaded into
the System Watchdog Service Register (SWSRR), starting the process over. When a new value is
loaded into SWTC, the software watchdog timer is not updated until the servicing sequence is
written to the SWSRR. If SWCRR[SWEN] is loaded with 0, the modulus counter does not count.
21.4 Timers Programming Model
Because they are programmed differently, the device-level, SC3400 DSP core platform level, and
software watchdog timers are described in separate subsections.
21.4.1 Device-Level Timers
This section describes the device-level timers. For a complete listing of all registers in all
modules with their memory locations, see Chapter 9, Memory Map. The device-level timer
registers are listed as follows, along with the pages on which the registers are discussed:
Timer Channel Control Registers (TMR[0–3]CTL[0–3], page 21-17.
Timer Channel Status and Control Registers (TMR[0–3]SCTL[0–3]), page 21-19.
Timer Channel Compare Register 1 (TMR[0–3]CMP1[0–3]), page 21-21.
Time-out
SWCNR
Reload
SWCRR[SWEN]
CLASS64
Clock
SWCRR[SWPR]
65536
Divider
Clock
Disable
SWSRR[WS]
SWCRR[SWTC]
Service
SWCRR[SWRI]
16-Bit Decrementer
Event
Logic
Reset
or MCP
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...