#22399: AR71xx / AR9331 UART not initialized
-------------------------------------------------+-------------------------
Reporter: mike@… | Owner: developers
Type: defect | Status: new
Priority: normal | Milestone:
Component: packages | Version: Trunk
Keywords: UART, serial, AR9331, AR933x, |
AR71xx, framing errors |
-------------------------------------------------+-------------------------
Issue:
Many TTL UART Devices do not work with this device during uBoot, but work
just fine once Linux initializes the port. During uBoot, all serial
output is "junk" with framing errors. The moment Linux inits the AR9331
UART correctly, everything works as expected.
Cause:
In uBoot, UART is not initialized per datasheet requirements. It simply
stuffs in the bit-rate and hopes for the best. It should a) enable, b)
"start", c) bit-rate, and d) parameter the UART before beginning
communication. Skipping enable and "start" causes jitter leading to
sampling errors. This also affects uplink and can cause checksum errors
when uploading firmware, leading to bricked devices.
Some RS232 TLL adapters overcome this on the downlink by deviating from
the EIA 232 standard and sampling outside of recommended timing. It is
not possible to overcome this on the uplink.
Piotr from the uBoot community has provided the following updated UART
routine which includes proper initialization. He's given permission to
patch the AR71xx tree with it.
https://github.com/pepe2k/u-boot_mod/blob/master/u-boot/cpu/mips/ar7240/qca_hs_uart.c
Patching is beyond my capabilities. Happy to support a fix any way I'm
able.
--
Ticket URL: <https://dev.openwrt.org/ticket/22399>
OpenWrt <http://openwrt.org>
Opensource Wireless Router Technology
_______________________________________________
openwrt-tickets mailing list
openwrt-tickets@lists.openwrt.org
https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-tickets
