UM10375 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
User manual Rev. 3 — 14 June 2011 56 of 368
NXP Semiconductors
UM10375
Chapter 5: LPC13xx Power profiles
The routine returns a result code that indicates if the system PLL was successfully set
(PLL_CMD_SUCCESS) or not (in which case the result code identifies what went wrong).
The current system frequency value is also returned. The application should use this
information to adjust other clocks in the device (the SSP, UART, and WDT clocks, and/or
clockout).
The following definitions are needed when making set_pll power routine calls:
/* set_pll mode options */
#define CPU_FREQ_EQU 0
#define CPU_FREQ_LTE 1
#define CPU_FREQ_GTE 2
#define CPU_FREQ_APPROX 3
/* set_pll result0 options */
#define PLL_CMD_SUCCESS 0
#define PLL_INVALID_FREQ 1
#define PLL_INVALID_MODE 2
#define PLL_FREQ_NOT_FOUND 3
#define PLL_NOT_LOCKED 4
For a simplified clock configuration scheme see Figure 7. For more details see Figure 3.
5.5.1.1 Param0: system PLL input frequency and Param1: expected system clock
set_pll looks for a setup in which the system PLL clock does not exceed 72 MHz. It easily
finds a solution when the ratio between the expected system clock and the system PLL
input frequency is an integer value, but it can also find solutions in other cases.
The system PLL input frequency (Param0) must be between 10000 to 25000 kHz (10
MHz to 25 MHz) inclusive. The expected system clock (Param1) must be between 1 and
72000 kHz inclusive. If either of these requirements is not met, set_pll returns
PLL_INVALID_FREQ and returns Param0 as Result1 since the PLL setting is unchanged.
5.5.1.2 Param2: mode
The first priority of set_pll is to find a setup that generates the system clock at exactly the
rate specified in Param1. If it is unlikely that an exact match can be found, input parameter
mode (Param2) should be used to specify if the actual system clock can be less than or
equal, greater than or equal or approximately the value specified as the expected system
clock (Param1).
A call specifying CPU_FREQ_EQU will only succeed if the PLL can output exactly the
frequency requested in Param1.
Table 64. set_pll routine
Routine set_pll
Input Param0: system PLL input frequency (in kHz)
Param1: expected system clock (in kHz)
Param2: mode (CPU_FREQ_EQU, CPU_FREQ_LTE, CPU_FREQ_GTE,
CPU_FREQ_APPROX)
Param3: system PLL lock time-out
Result Result0: PLL_CMD_SUCCESS | PLL_INVALID_FREQ | PLL_INVALID_MODE |
PLL_FREQ_NOT_FOUND | PLL_NOT_LOCKED
Result1: system clock (in kHz)
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