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codebot committed Sep 25, 2018
1 parent 1351a0e commit 1d44a47ef8c4b938241f8203a828895dab778491
Showing with 19 additions and 7 deletions.
  1. +19 −7 doc/ovc2a/README.md
  2. BIN doc/ovc2a/ovc2a_mobo_right.png
@@ -5,15 +5,27 @@
Here is a rendering of the bottom of the TX2 carrier board:
![tx2-peripherals](https://github.com/osrf/ovc/raw/master/doc/ovc2a/ovc2a_mobo_bottom.png "TX2 peripherals")

The right-hand side (the side with the two buttons) has several UARTs:
* UART0 is the Linux root console.
* UART2 is available for userland use
* UART3 is available for userland use
Here is a rendering of the right-hand side (the side with two buttons), which
is probably more useful of the OVC2a is already in a case:
![tx2-peripherals-right](https://github.com/osrf/ovc/raw/master/doc/ovc2a/ovc2a_mobo_right.png "TX2 right-side peripherals")

Those UARTs are all buffered to 3.3v, but should still be treated as
static-sensitive since they do not have ESD clamp diodes.
There are several UARTs provided by the TX2:
* TX2 UART0 (TX0, RX0) is the Linux root console. You can use it to catch the bootloader, fix network issues if DHCP isn't working, enter WiFi credentials, etc.
* TX2 UART1 is internally connected to the IMU and appears in userland as `/dev/ttyTHS2`
* TX2 UART2 (TX2, RX2) is available for userland use
* TX2 UART3 (TX3, RX3) is available for userland use

They should appear in userland as `/dev/ttyTHS2` and `/dev/ttyTHS3`
Those UARTs are all buffered to 3.3v, but should still be treated as
static-sensitive since they do not have ESD clamp diodes. Although there are
device nodes for the "classic" names such as `/dev/ttyS2`, etc., it's much
better to use the DMA-accelerated device nodes instead, which have `THS` in
them, such as `/dev/ttyTHS2`, to avoid unnecessary kernel switches for things
as silly as feeding the next character to the UART.

TX2 UART2 and UART3 should be mapped to `/dev/ttyTHS` nodes, but I can't
remember which ones right now; it's usually a process of trial and error. It's
possible that one (or both) of them will require a device tree modification,
but I can't be sure at the moment.

### Ethernet

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