Logging CPU load by top command per minute with BusyBox command environment

start.sh

#!/bin/sh
## if you want to run toplog_per_minute.sh in background
## you have to use leading script to put it into backgroud without 
## issue of "Stopped (tty output)" Error Message of script that 
## stucked on busybox top command
## tested in BusyBox v1.20.2
##################################################################
/bin/sh /mnt/nand/toplog_per_minute.sh &

toplog_per_minute.sh

#!/bin/sh
TARGET_PREFIX=/mnt/mmc0/toplog
LOG_INTERVAL=60

run_top_once()
{
  DATESTR="`date +'%Y%m%d-%H:%M:%S'`"
  DATEONLY="${DATESTR:0:8}"
  if [ "$DATEONLY" = "19700101" ]; then
    return
  fi
  top_logname="${TARGET_PREFIX}${DATEONLY}.txt"
  echo "D$DATESTR" >> $top_logname
  top -b -n 1 >> $top_logname
  ## if you also want to log memory, please uncomment the next line
  # free >> $top_logname
}

while [ 1 ] ; do
  run_top_once ; sleep $LOG_INTERVAL;
done