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Pablo Rodriguez

Jun 27, 2018, 12:13:55 PM6/27/18
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I'm testing rs485 without success with this image Debian Testing (Buster) 2018-06-17 4GB SD IoT , kernel 4.14.49-ti-r54.

This are the overlay in uEnv.txt
###Overide capes with eeprom

 cat /proc/tty/driver/serial

0: uart:8250 mmio:0x44E09000 irq:30 tx:460 rx:3 brk:3 RTS|CTS|DTR|DSR
1: uart:unknown port:00000000 irq:0
2: uart:unknown port:00000000 irq:0
3: uart:unknown port:00000000 irq:0
4: uart:8250 mmio:0x481A8000 irq:31 tx:0 rx:0 CTS|DSR
5: uart:unknown port:00000000 irq:0

at boot time i'm no seeing errors with the overlays.

boot_overlays: loading /lib/firmware/BB-UART5-RTSCTS-00A0.dtbo ...
924 bytes read in 336 ms (2 KiB/s)
uboot_overlays: loading /lib/firmware/BB-UART4-RS485-00A0.dtbo ...
1105 bytes read in 341 ms (2.9 KiB/s)

Can anyone confim if the rs485 capabilities were added to the 8250 driver or must use OMAP driver.
with omap driver is mandatory to use 3.8.13 kernel?

Thanks in advance

Jeff Andich

Jun 27, 2018, 2:24:39 PM6/27/18
to BeagleBoard
I can confirm that you can use the OMAP driver with kernel version, 4.4.110, as that's what we're using right now to implement RS485 on a custom board based on the BB-X15.  For that platform, we started with the 01-01-2018 BB-X15 debian (8.10) console image, and substituted the kernel built with the OMAP drivers.

For the OMAP driver we found that you need to use a GPIO for the RTS line or the signal which toggles the DE on the 485 chip.  In order to switch to the OMAP driver, you have to change a number of defines in the kernel config to switch off the 8250 and switch on the OMAP driver, and make sure that console port is using the OMAP driver.

We still have yet to try a later kernel where 485 was ported to the 8250 driver.
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