AM3356: Inquiry about flexible changing CPU speed

Takayuki Miyazaki

Part Number: AM3356

Hi Experts,

Customer is developing their system with AM3356BZCZA80(Linux SDK version:06_03_00_106)/TPS65910AA1RSLR. In their current system, Cortex-A8 is working at 600MHz/VDD_CORE=1.1V. Recently, their End-customer is requesting to reduce bootup/startup time. Therefore, customer is considering they would like to operate at 800HMz from powerup. After bootup/startup, customer is also considering that the operating clock frequency is changed to 600MHz dynamically, because of reducing power-consumption.

According to Datasheet " Table 5-7. VDD_MPU OPPs for ZCZ Package". If Cortex-A8 is operating at 800MHz, customer has to supply not "VDD_MPU = 1.1V" but "VDD_MPU = 1.26V". it means, it seems that customer needs to control PMIC.

Customer is asking if TI Linux SDK is supporting the above control(CPU speed/VDD_MPU voltage)? Is it possible to change CPU speed/VDD_MPU voltage dynamically? Can I have your Expert's advice/comments on this, please?

If there is any solution which reduces bootup/startup time, could you share it, please?

Best regards,

Miyazaki

over 4 years ago

0 Bin Liu over 4 years ago

TI__Guru*** 148401 points

Hi Miyazaki-san,

Your query has been assigned to the expert. Due to US holidays, the response will be delayed.

0 Hong Guan64 over 4 years ago in reply to Bin Liu

TI__Guru 62615 points

Hi Miyazaki-san,
#1. max speed auto-detection in SPL
On AM335x, SPL sets the max speed supported by the device based on reading CM EFUSE_SMA register @44E107Fc.
An example reading @u-boot prompt on 1GHz part is listed below for your reference:

=> md 0x44E107Fc 1
44e107fc: 00013c2f

#2. PMIC configuration in SPL
PMIC is configured in SPL board file "/board/ti/am335x/board.c" based on the max speed detected, specifically in function

void scale_vcores_generic(int freq){
...
	/*
	 * The GP EVM, IDK and EVM SK use a TPS65910 PMIC.  For all
	 * MPU frequencies we support we use a CORE voltage of
	 * 1.10V.  For MPU voltage we need to switch based on
	 * the frequency we are running at.
	 */
...
}

#3. Linux DVFS
When Dynamic Voltage and Frequency Scaling (DVFS) is enabled, Linux kernel dynamically scale the voltage and frequency based on need,
user preference, or other factors. Please refer the following link for details on DVFS framework.
software-dl.ti.com/.../Power_Management.html
I captured a sample log for DVFS on AM335x GP EVM with 1GHz part, and uploaded it in attachment for your reference

Best,

-Hong

7853.am3_gp_6.3_dvfs.txt

devmem2 0x44e107fc
/dev/mem opened.
Memory mapped at address 0xb6efe000.
Read at address  0x44E107FC (0xb6efe7fc): 0x00013C2F
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available__frequencies
300000 600000 720000 800000 1000000 
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
600000
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
600000
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available__governors
conservative userspace powersave ondemand performance 
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
cpufreq-dt
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/stats/trans_table 
   From  :    To
         :    300000    600000    720000    800000   1000000 
   300000:         0       129        14        15        59 
   600000:       126         0         9         7        44 
   720000:        20         7         0         4        21 
   800000:        22         9         2         0        29 
  1000000:        49        42        27        36         0 
root@am335x-hs-evm:~# cat /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_statte
300000 79303
600000 610
720000 131
800000 186
1000000 3556
root@am335x-hs-evm:~#

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AM3356: Inquiry about flexible changing CPU speed