
Clock Generation Module (CGM)
Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
Freescale Semiconductor
7-3
During assertion of a hardware reset, the value of the PINIT input pin is written into the PCTL PLL Enable
(PEN) bit. After a hardware reset is de-asserted, a write operation to PCTL will change the PEN bit
accordingly, and the PLL will then ignore the PINIT pin.
During reset, the system clock is bypassed to extal.
After reset, if PINIT = 0 then the PLL will be in bypass mode and the system clock becomes extal
immediately. Otherwise, the PLL is in normal function mode and the system will be driven by the PLL
output clock after a PLL lock time (< 0.2 ms).
For the sake of power-saving, the CGM can switch to WAIT or STOP modes whenever the DSP Cores
execute corresponding commands. The device can get out of WAIT and STOP modes if it gets the
corresponding interrupts.
Table 7-1. System Clock Definition
Scenario
PLL.PD
PLL.BP
Other
Config
PLL.LD
CGM Clock
1
1
CGM Clock: the clocks in CGM module. It is always active for proper switching and wake-up.
System Clock
2
2
System Clock: the clock used by all DSP56724/DSP56725 modules.
Core
Cock
Peripheral
Clock
During
Reset
pinit_nmi = 1
0
1
By default
0
3
3
The PLL.LD will be low if the PLL doesn’t detect a lock condition.
Fosc
Fosc
Fosc
pinit_nmi = 0
After
Reset
PLL
Normal
mode
4
4
The mode that PLL will get into after reset, normal mode or bypass mode, is decided by the PINIT_NMI pin during reset.
Before PLL.LD
0
0
–
0
Fosc
0
0
After PLL.LD
0
0
–
1
Target
Target
5
5
Target: the frequency (user-configured) in the PCTL register.
Target
PLL Bypass mode
6
6
It is the PLL’s bypass mode. It is configured by either Core-0 or Core-1, over the Shared Peripheral bus.
0
1
–
0
Fosc
Fosc
Fosc
System Wait mode
0
0/1
7
7
It is NOT a conflict if the PLL is in bypass mode while the system is in wait mode.
–
0/1
Fosc/Target
0
8
8
In wait mode, for power saving, the Core clock is stopped even though the Peripheral clock is still active.
Fosc/Target
System Stop mode
pstp
9
9
Whether the PLL should be powered down or not in stop mode is decided by the PSTP bit in the PCTL register.
0/1
10
10
It’s NOT a conflict if the PLL is in bypass mode while the system is in stop mode.
–
0/1
Fosc/Target
0
0