The only UART connected on the S30 is the UART1 (ttyS1). In order to get the uart to produce any output you need to change the U-boot configuration to redirect the output to that UART. In order to do so you need to change the following:

• Modify the DTS to replace any uart0 mentions to uart1, also change the pins to uart1_pins_a
• Modify the u-boot config:
  • CONFIG_CONS_INDEX = 2 (switches to UART1)
  • CONFIG_MMC0_CD_PIN=”” (enables booting via SDcard)

You can find an initial version of the PocketGo-S30 DTS here.