Clocks
119
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Architecture
2.4.3.3
Selecting Clock Source Upon Wake Up
The domains for CPU clock (GCLK), the system clock (HCLK) and the peripheral clock (VCLKx) use the
same clock source selected via the GHVSRC field of the GHVSRC register. The GHVSRC register also
allows the application to choose the clock source after wake up via the GHVWAKE field.
When a wake up condition is detected, if the selected wake up clock source is not already active, the
global clock module (GCM) will enable this selected clock source, wait for it to become valid, and then use
it for the GCLK, HCLK and VCLKx domains. The other clock domains VCLKAx and RTICLK retain the
configuration for their clock source selection registers – VCLKASRC, VCLKACON1 and RCLKSRC.
2.4.4 Clock Test Mode
The RM48x microcontrollers support a test mode which allows a user to bring out several different clock
sources and clock domains on to the ECLK terminal. This is very useful information for debug purposes.
Each clock source also has a corresponding clock source valid status flag in the Clock Source Valid
Status (CSVSTAT) register. The clock source valid status flags can also be brought out on to the
NHET1[12] terminal in this clock test mode.
The clock test mode is controlled by the CLKTEST register in the system module register frame.
Figure 2-4. Clock Test Register (CLKTEST) [offset = FFFF FFF8Ch]
31
27
26
25
24
Reserved
ALTLIMPCLOCK
ENABLE
RANGEDET
CTRL
RANGEDET
ENASSEL
R-0
R/WP-0
R/WP-0
R/WP-0
23
20
19
16
Reserved
CLK_TEST_EN
R-0
R/WP-Ah
15
12
11
8
7
4
3
0
Reserved
SEL_GIO_PIN
Reserved
SEL_ECP_PIN
R-0
R/WP-0
R-0
R/WP-0
LEGEND: R/W = Read/Write; R = Read only; WP = Write in privileged mode only; -
n
= value after reset
The clock test mode is enabled by writing 5h to the CLK_TEST_EN field.
The signal to be brought out on to the ECLK terminal is defined by the SEL_ECP_PIN field, and the signal
to be brought out on to the NHET1[12] terminal is defined by the SEL_GIO_PIN field.
The choices for these selections are defined in
.
Table 2-12. Clock Test Mode Options
SEL_ECP_PIN
Signal on ECLK
SEL_GIO_PIN
Signal on NHET1[12]
0000
Oscillator
0000
Oscillator Valid status
0001
PLL1 free-running clock output
0001
PLL1 Valid status
0010
Reserved
0010
Reserved
0011
EXTCLKIN1
0011
Reserved
0100
Low-frequency LPO
(Low-Power Oscillator) clock
0100
Reserved
0101
High-frequency LPO
(Low-Power Oscillator) clock
0101
HF LPO Valid status
0110
PLL2 free-running clock output
0110
PLL2 Valid status
0111
EXTCLKIN2
0111
Reserved
1000
GCLK
1000
LF LPO Valid status
1001
RTI Base
1001
Reserved
1010
Reserved
1010
Reserved