Calibrate udelay for PinePhone NuttX

nuttx-pinephone-udelay.log

DRAM: 2048 MiB
Trying to boot from MMC1
NOTICE:  BL31: v2.2(release):v2.2-904-gf9ea3a629
NOTICE:  BL31: Built : 15:32:12, Apr  9 2020
NOTICE:  BL31: Detected Allwinner A64/H64/R18 SoC (1689)
NOTICE:  BL31: Found U-Boot DTB at 0x4064410, model: PinePhone
NOTICE:  PSCI: System suspend is unavailable


U-Boot 2020.07 (Nov 08 2020 - 00:15:12 +0100)

DRAM:  2 GiB
MMC:   Device 'mmc@1c11000': seq 1 is in use by 'mmc@1c10000'
mmc@1c0f000: 0, mmc@1c10000: 2, mmc@1c11000: 1
Loading Environment from FAT... *** Warning - bad CRC, using default environment

starting USB...
No working controllers found
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
Found U-Boot script /boot.scr
653 bytes read in 3 ms (211.9 KiB/s)
## Executing script at 4fc00000
gpio: pin 114 (gpio 114) value is 1
183460 bytes read in 11 ms (15.9 MiB/s)
Uncompressed size: 20062208 = 0x1322000
36162 bytes read in 4 ms (8.6 MiB/s)
1078500 bytes read in 51 ms (20.2 MiB/s)
## Flattened Device Tree blob at 4fa00000
   Booting using the fdt blob at 0x4fa00000
   Loading Ramdisk to 49ef8000, end 49fff4e4 ... OK
   Loading Device Tree to 0000000049eec000, end 0000000049ef7d41 ... OK

Starting kernel ...

- Ready to Boot CPU
- Boot from EL2
- Boot from EL1
- Boot to C runtime for OS Initialize
nsh: sysinit: fopen failed: 2
nsh: mkfatfs: command not found

NuttShell (NSH) NuttX-11.0.0-pinephone
nsh> ?
help usage:  help [-v] [<cmd>]

  .         cd        dmesg     free      mkrd      reboot    test      unset     
  [         cp        echo      help      mount     rm        time      uptime    
  ?         cmp       env       hexdump   mv        rmdir     true      usleep    
  basename  dirname   exec      kill      printf    set       truncate  xd        
  break     dd        exit      ls        ps        sleep     uname     
  cat       df        false     mkdir     pwd       source    umount    

Builtin Apps:
  calib_udelay  hello         nsh           sh            
  getprime      leds          ostest        
nsh> 
nsh> calib_udelay

Calibrating timer for main calibration...
Performing main calibration for udelay.This will take approx. 17.280 seconds.
Calibration slope for udelay:
  Y = m*X + b, where
    X is loop iterations,
    Y is time in nanoseconds,
    b is base overhead,
    m is nanoseconds per loop iteration.

  m = 8.58195489 nsec/iter
  b = -347067.66917297 nsec

  Correlation coefficient, R² = 1.0000

Without overhead, 0.11652356 iterations per nanosecond and 116523.57 iterations per millisecond.

Recommended setting for CONFIG_BOARD_LOOPSPERMSEC:
   CONFIG_BOARD_LOOPSPERMSEC=116524
nsh> 
nsh>