found on [[https://www.eevblog.com/forum/repair/trying-to-troubleshoot-a-main-board-with-rockchip-rk3288-microprocessor/|eevBlog]]

To get a backup console access in case of fail  -- you need a RS232 accss to the unit

<code>
$>printenv bootargs
$>bootargs=root=PARTUUID=24d1deac-3434-1a4e-98d1-68ee2945a5f1 rootwait ro console=ttyS2,115200 rfkill.default_state=0
$>setenv bootargs 'root=PARTUUID=24d1deac-3434-1a4e-98d1-68ee2945a5f1 rootwait ro console=ttyS2,115200 rfkill.default_state=0 single init=/bin/sh'
$>boot
$>mount -rw -o remount /
$>passwd root
$>reboot -f
</code>


To list mmc : 
<code>
=> mmc list
dwmmc@ff0f0000: 0 (eMMC)
</code>

to choose mmc dev :
<code>
=> mmc dev 0
switch to partitions #0, OK
mmc0(part 0) is current device
</code>

to get mmc info : 
<code>
=> mmcinfo
Device: dwmmc@ff0f0000
Manufacturer ID: 45
OEM: 100
Name: DG400
Tran Speed: 52000000
Rd Block Len: 512
MMC version 4.0
High Capacity: Yes
Capacity: 7.3 GiB
Bus Width: 8-bit
Erase Group Size: 512 KiB
</code>