Processor Frequency (speed)

# 19 Apr 2012

Dear all,

May I know how can I change the processor speed in mbed? I want to run mbed at 60MHz, 100MHz and in overclocked mode. Please help me with this

Thanks

Herson Bagay

# 19 Apr 2012

Here's a link to the LPC1768 user manual. It describes the details on what needs to be done to change the MCU's clock speed. It's on chapter 4.

http://www.nxp.com/documents/user_manual/UM10360.pdf

The basic steps normally include turning the HSE, setting the PLL multipliers, using the HSE as the PLL source, and switching the sysclock source to the PLL to change a clock speed

S N

# 19 Apr 2012

Thank you very much. But if I don't configure anything (for ex, hello world program given in this site) here in the compiler for mbed, the processor will run at 12MHz. right?

Herson Bagay

# 19 Apr 2012

it runs on 96MHz I believe. Somewhere in the initialization library sets it to that speed

Wen qian

# 19 Apr 2012

Hello Sujay,

You can try to refer this link

mbed.org/forum/mbed/topic/229/?page=1

Hope this will help you.

:)

Adam Green

# 24 Apr 2012

This is a recent dump of the SystemInit() routine used for the mbed1768 with my comments.

; SystemInit (from capi.ar)
; Initializes the LPC1768 clocks and peripherals
SystemInit:
; Set base pointer (r0) to 0x400FC000
00001D50  481B       LDR R0, .+112 ; .+112 == 0x1DC0
; Enable main oscillator
00001D52  2120       MOVS R1, #32 ; 32 == 0x20
00001D54  F8C0 11A0  STR.W R1, [R0, #+416] ; +416 == +0x1A0
; Wait for main oscillator to stabilize
00001D58  F8D0 11A0  LDR.W R1, [R0, #+416] ; +416 == +0x1A0
00001D5C  F011 0F40  TST R1, #0x00000040
00001D60  D0FA       BEQ .-8 ; .-8 == 0x1D58
; Set CPU clock to PLL0 / 3 = 288 MHz / 3 = 96 MHz
00001D62  2102       MOVS R1, #2 ; 2 == 0x2
00001D64  F8C0 1104  STR.W R1, [R0, #+260] ; +260 == +0x104
; Configure PLL0 to use main oscillator as its input
00001D68  2101       MOVS R1, #1 ; 1 == 0x1
00001D6A  F8C0 110C  STR.W R1, [R0, #+268] ; +268 == +0x10C
; PLL0 multiplier set to 11+1=12  12 MHz * 12 * 2 = 288 MHz
00001D6E  220B       MOVS R2, #11 ; 11 == 0xB
00001D70  F8C0 2084  STR.W R2, [R0, #+132] ; +132 == +0x84
; Set enable for PLL0 but not completed until the PLL is fed
00001D74  F8C0 1080  STR.W R1, [R0, #+128] ; +128 == +0x80
; Feed PLL0
00001D78  22AA       MOVS R2, #170 ; 170 == 0xAA
00001D7A  F8C0 208C  STR.W R2, [R0, #+140] ; +140 == +0x8C
00001D7E  2355       MOVS R3, #85 ; 85 == 0x55
00001D80  F8C0 308C  STR.W R3, [R0, #+140] ; +140 == +0x8C
; Wait for PLL0 to lock
00001D84  F8D0 1088  LDR.W R1, [R0, #+136] ; +136 == +0x88
00001D88  F011 6F80  TST R1, #0x04000000
00001D8C  D0FA       BEQ .-8 ; .-8 == 0x1D84
; Set bit to connect PLL0 but not completed until PLL is fed
00001D8E  2103       MOVS R1, #3 ; 3 == 0x3
00001D90  F8C0 1080  STR.W R1, [R0, #+128] ; +128 == +0x80
; Feed PLL0
00001D94  F8C0 208C  STR.W R2, [R0, #+140] ; +140 == +0x8C
00001D98  F8C0 308C  STR.W R3, [R0, #+140] ; +140 == +0x8C
; Set USB clock to PLL0 clock divided by 5+1=6  288 MHz / 6 = 48 MHz
00001D9C  2105       MOVS R1, #5 ; 5 == 0x5
00001D9E  F8C0 1108  STR.W R1, [R0, #+264] ; +264 == +0x108
; Set all peripheral clocks to PLL0 / 4  288 MHz / 4 = 72 MHz
00001DA2  2100       MOVS R1, #0 ; 0 == 0x0
00001DA4  F8C0 11A8  STR.W R1, [R0, #+424] ; +424 == +0x1A8
00001DA8  F8C0 11AC  STR.W R1, [R0, #+428] ; +428 == +0x1AC
; Enable all peripherals by writing 0x042887DE to 0x400FC0C4
00001DAC  4A05       LDR R2, .+24 ; .+24 == 0x1DC4
00001DAE  F8C0 20C4  STR.W R2, [R0, #+196] ; +196 == +0xC4
; Set external CLKOUT signal to CPU Clock
00001DB2  F8C0 11C8  STR.W R1, [R0, #+456] ; +456 == +0x1C8
; Set FLASH MAM to use 4 clocks
00001DB6  F243 013A  MOVW R1, #0x303A ; 0x303A == 12346
00001DBA  6001       STR R1, [R0, #0] ; 0 == 0x0
; Return to caller
00001DBC  4770       BX LR
; Function literals
00001DBE  0000       DCWU 0x0000        ; Padding for 4-byte alignment
00001DC0  C000 400F  DCDU 0x400FC000    ; Base pointer for system control registers
00001DC4  87DE 0428  DCDU 0x042887DE    ; Value used to enable all peripherals

This is a recent dump of the SystemInit() routine used for the mbed1768 with my comments. <<code>> ; SystemInit (from capi.ar) ; Initializes the LPC1768 clocks and peripherals SystemInit: ; Set base pointer (r0) to 0x400FC000 00001D50 481B LDR R0, .+112 ; .+112 == 0x1DC0 ; Enable main oscillator 00001D52 2120 MOVS R1, #32 ; 32 == 0x20 00001D54 F8C0 11A0 STR.W R1, [R0, #+416] ; +416 == +0x1A0 ; Wait for main oscillator to stabilize 00001D58 F8D0 11A0 LDR.W R1, [R0, #+416] ; +416 == +0x1A0 00001D5C F011 0F40 TST R1, #0x00000040 00001D60 D0FA BEQ .-8 ; .-8 == 0x1D58 ; Set CPU clock to PLL0 / 3 = 288 MHz / 3 = 96 MHz 00001D62 2102 MOVS R1, #2 ; 2 == 0x2 00001D64 F8C0 1104 STR.W R1, [R0, #+260] ; +260 == +0x104 ; Configure PLL0 to use main oscillator as its input 00001D68 2101 MOVS R1, #1 ; 1 == 0x1 00001D6A F8C0 110C STR.W R1, [R0, #+268] ; +268 == +0x10C ; PLL0 multiplier set to 11+1=12 12 MHz * 12 * 2 = 288 MHz 00001D6E 220B MOVS R2, #11 ; 11 == 0xB 00001D70 F8C0 2084 STR.W R2, [R0, #+132] ; +132 == +0x84 ; Set enable for PLL0 but not completed until the PLL is fed 00001D74 F8C0 1080 STR.W R1, [R0, #+128] ; +128 == +0x80 ; Feed PLL0 00001D78 22AA MOVS R2, #170 ; 170 == 0xAA 00001D7A F8C0 208C STR.W R2, [R0, #+140] ; +140 == +0x8C 00001D7E 2355 MOVS R3, #85 ; 85 == 0x55 00001D80 F8C0 308C STR.W R3, [R0, #+140] ; +140 == +0x8C ; Wait for PLL0 to lock 00001D84 F8D0 1088 LDR.W R1, [R0, #+136] ; +136 == +0x88 00001D88 F011 6F80 TST R1, #0x04000000 00001D8C D0FA BEQ .-8 ; .-8 == 0x1D84 ; Set bit to connect PLL0 but not completed until PLL is fed 00001D8E 2103 MOVS R1, #3 ; 3 == 0x3 00001D90 F8C0 1080 STR.W R1, [R0, #+128] ; +128 == +0x80 ; Feed PLL0 00001D94 F8C0 208C STR.W R2, [R0, #+140] ; +140 == +0x8C 00001D98 F8C0 308C STR.W R3, [R0, #+140] ; +140 == +0x8C ; Set USB clock to PLL0 clock divided by 5+1=6 288 MHz / 6 = 48 MHz 00001D9C 2105 MOVS R1, #5 ; 5 == 0x5 00001D9E F8C0 1108 STR.W R1, [R0, #+264] ; +264 == +0x108 ; Set all peripheral clocks to PLL0 / 4 288 MHz / 4 = 72 MHz 00001DA2 2100 MOVS R1, #0 ; 0 == 0x0 00001DA4 F8C0 11A8 STR.W R1, [R0, #+424] ; +424 == +0x1A8 00001DA8 F8C0 11AC STR.W R1, [R0, #+428] ; +428 == +0x1AC ; Enable all peripherals by writing 0x042887DE to 0x400FC0C4 00001DAC 4A05 LDR R2, .+24 ; .+24 == 0x1DC4 00001DAE F8C0 20C4 STR.W R2, [R0, #+196] ; +196 == +0xC4 ; Set external CLKOUT signal to CPU Clock 00001DB2 F8C0 11C8 STR.W R1, [R0, #+456] ; +456 == +0x1C8 ; Set FLASH MAM to use 4 clocks 00001DB6 F243 013A MOVW R1, #0x303A ; 0x303A == 12346 00001DBA 6001 STR R1, [R0, #0] ; 0 == 0x0 ; Return to caller 00001DBC 4770 BX LR ; Function literals 00001DBE 0000 DCWU 0x0000 ; Padding for 4-byte alignment 00001DC0 C000 400F DCDU 0x400FC000 ; Base pointer for system control registers 00001DC4 87DE 0428 DCDU 0x042887DE ; Value used to enable all peripherals <</code>>

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