# filesystem activity
fatrace -t -f W

# check benchmark
dd if=/dev/mmcblk2 of=/dev/null bs=1M count=512 iflag=direct

cat /sys/kernel/debug/mmc1/ios
clock:          200000000 Hz
actual clock:   200000000 Hz
vdd:            16 (2.8 ~ 2.9 V)
bus mode:       2 (push-pull)
chip select:    0 (don't care)
power mode:     2 (on)
bus width:      2 (4 bits)
timing spec:    6 (sd uhs SDR104)
signal voltage: 1 (1.80 V)
driver type:    0 (driver type B)