[U-Boot] [PATCH] At start of autoboot check, flush any pending RX bytes

[Robert Nelson]

On Thu, Jan 14, 2016 at 11:31 AM, Tom Rini <trini at konsulko.com> wrote:

> On Mon, Jan 11, 2016 at 09:59:18AM -0700, Simon Glass wrote:
> > Hi Craig,
> >
> > On 20 December 2015 at 19:07, Craig McQueen
> > <craig.mcqueen at innerrange.com> wrote:
> > > This is to avoid the boot sequence halting due to initial "junk"
> > > received on serial input.
> > >
> > > Signed-off-by: Craig McQueen <craig.mcqueen at innerrange.com>
> > > ---
> > > I have found that on the BeagleBone Black, U-Boot occasionally halts at
> > > the U-Boot prompt at boot-up, whether power-up, warm external
> > > reset or software reset. I have seen other people report the same
> issue.
> > >
> > > This seems to be due to U-Boot receiving "junk" data on the serial
> > > console. The BeagleBone Black has a pull-down resistor which was
> > > apparently added to try to mitigate this issue, but it doesn't entirely
> > > fix it.
> >
> > I wonder if this can be fixed for that board only?
>
> No, and it's not -exactly- a that board only problem.  It's a HW design
> issue that can show up elsewhere too.  I _think_ however in this case
> the answer would be to migrate to perhaps CONFIG_AUTOBOOT_KEYED_CTRLC as
> that's one of the reason various other boards use that set of options.
>
> I would suggest bringing this up on the beaglebone list to see what the
> various people that ship and support these boards think, thanks!
>

I actually enabled this feature this week by default for beagleboard.org:

diff --git a/configs/am335x_evm_defconfig b/configs/am335x_evm_defconfig
index 27cb881..8699953 100644
--- a/configs/am335x_evm_defconfig
+++ b/configs/am335x_evm_defconfig
@@ -3,7 +3,10 @@ CONFIG_TARGET_AM335X_EVM=y
 CONFIG_SPL_STACK_R_ADDR=0x82000000
 CONFIG_SPL=y
 CONFIG_SPL_STACK_R=y
-CONFIG_SYS_EXTRA_OPTIONS="NAND"
+CONFIG_AUTOBOOT_KEYED=y
+CONFIG_AUTOBOOT_PROMPT="Press SPACE to abort autoboot in %d seconds\n"
+CONFIG_AUTOBOOT_DELAY_STR="d"
+CONFIG_AUTOBOOT_STOP_STR=" "
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y

It'll take time to replace older images but on target users can just:

cd /opt/scripts/tools/developers/
git pull
sudo ./update_bootloader.sh

U-Boot SPL 2016.01-00001-g4eb802e (Jan 13 2016 - 11:14:31)
Trying to boot from MMC
bad magic


U-Boot 2016.01-00001-g4eb802e (Jan 13 2016 - 11:14:31 -0600), Build:
jenkins-github_Bootloader-Builder-313

       Watchdog enabled
I2C:   ready
DRAM:  512 MiB
Reset Source: Global external warm reset has occurred.
Reset Source: Power-on reset has occurred.
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Using default environment

Net:   <ethaddr> not set. Validating first E-fuse MAC
cpsw, usb_ether
Press SPACE to abort autoboot in 2 seconds
=>


Regards,

-- 
Robert Nelson
https://rcn-ee.com/