Hi Alex,
I had time to conduct one experiment. I modified /media/realroot/boot/grub/grub.conf file and replaced ttyS1 with ttyS0 as shown below. One behavior changed, I did not see the boot process via the 3.5mm stereo jack, but when ultimately booted I got the Linux prompt via my PC with the stereo jack on PuTTY set to 9600 baud, but the RS232 terminal isn't getting any signal. Once booted is there some other configuration file that resets Linux access back to ttyS1?
Below is my grub.conf, set to ttyS0, and connects to my PC via the stereo jack using PuTTY set at 9600 baud...
When I return in a few days from travel I can try the sketch serial code experiment unless other ideas are offered… thank you… John
default 2
timeout 1
title Clanton SVP kernel-SPI initrd-SPI IMR-On IO-APIC/HPET NoEMU
kernel --spi root=/dev/ram0 console=ttyS0,9600n8 earlycon=uart8250,mmio32,0x8010f000,115200n8 reboot=efi,warm apic=debug rw
initrd --spi
title Clanton SVP kernel-SPI rootfs-SD IMR-On IO-APIC/HPET NoEMU
root (hd0,0)
kernel /bzImage root=/dev/mmcblk0p2 console=ttyS0,9600n8 earlycon=uart8250,mmio32,0x9000b000,115200n8 reboot=efi,warm apic=debug rw rootwait quiet
title Clanton SVP kernel-MassStorage initrd-MassStorage big-rootfs IMR-On IO-APIC/HPET NoEMU debug
root (hd0,0)
kernel /bzImage root=/dev/ram0 console=ttyS0,9600n8 earlycon=uart8250,mmio32,0x8010f000,115200n8 reboot=efi,warm apic=debug rw LABEL=boot debugshell=5
initrd /core-image-minimal-initramfs-clanton.cpio.gz
