Disable interactive propmpt in extlinux

I have a GPS connected to uart0, and the input stream is interrupting the syslinux boot process when I get to the prompt regarding the kernel choice.

switch to partitions #0, OK
mmc1 is current device
Scanning mmc 1:1...
switch to partitions #0, OK
mmc0(part 0) is current device
Scanning mmc 0:1...
Found /boot/extlinux/extlinux.conf
Retrieving file: /boot/extlinux/extlinux.conf
221 bytes read in 160 ms (1000 Bytes/s)
p2771-0000 eMMC boot options
1:	primary kernel
Enter choice: 1

I need to get rid of the prompt which asks which kernel I want. The data from the GPS is streaming over that rx pin, and the boot sequence thinks I’m asking it to interrupt things. I’ve tried a number of options in /boot/extlinux/extlinux.conf, but nothing has worked so far.

I would really appreciate it if anyone had a suggestion. Thank you!

Keep in mind as you do this that procedures for modifying device tree and boot loader change depending on which release you use (it isn’t known which release you are using, nor if you are using the development carrier board…but it sounds like the dev carrier). The following URL talks about changing serial console from the original UART to a new UART, but if you simply don’t enable the other UART, then you are essentially removing serial console:

The bootloader stage has its own serial console code, and Linux itself has separate code. You need to disable both. Linux stage is easy, the bootloader is going to be a bit more effort. If you use the developer carrier board, then if you can use J17 instead of removing the J21 serial console your life will be much easier. If you do need J17, then following the instructions to remove serial console from J21 will do the trick.