Provide more compile time configurables for the UART control port

* MOTEUS_UART_DEFAULT_COMMAND_BAUD_RATE - does the obvious
* MOTEUS_R4_AUX2_RT - switches the two non-connectorized aux2 pins on
  moteus-r4 to be the R and T pads instead of the DBG1/2 pads

Author: jpieper

fw/aux_common.h

@@ -19,6 +19,10 @@
 
 #include "mjlib/base/visitor.h"
 
+#ifndef MOTEUS_UART_DEFAULT_COMMAND_BAUD_RATE
+#define MOTEUS_UART_DEFAULT_COMMAND_BAUD_RATE 1000000
+#endif
+
 namespace moteus {
 namespace aux {
 
@@ -101,7 +105,7 @@ struct UartEncoder {
     };
     Mode mode = kBoardDefault;
 
-    int32_t baud_rate = 1000000;
+    int32_t baud_rate = MOTEUS_UART_DEFAULT_COMMAND_BAUD_RATE;
     int32_t poll_rate_us = 100;
     uint8_t cui_amt21_address = 0x54;
 

fw/moteus_controller.cc

@@ -426,8 +426,17 @@ aux::AuxHardwareConfig GetAux2HardwareConfig() {
           //          ADC#  CHN    I2C      SPI      USART    TIMER
           { 0, PB_8,   -1,   0,    I2C1,    nullptr, USART3,  nullptr },
           { 1, PB_9,   -1,   0,    I2C1,    nullptr, USART3,  nullptr },
+          // Select which two stm32 pins are used for the
+          // non-connectorized aux2 pins for moteus-r4.  By default,
+          // the DBG1/DBG2, but if MOTEUS_R4_AUX2_RT is
+          // defined, then they will be the R and T pads.
+#ifndef MOTEUS_R4_AUX2_RT
           { 2, PC_14,  -1,   0,    nullptr, nullptr, nullptr, nullptr },
           { 3, PC_15,  -1,   0,    nullptr, nullptr, nullptr, nullptr },
+#else
+          { 2, PC_10,  -1,   0,    nullptr, nullptr, USART3, nullptr },
+          { 3, PC_11,  -1,   0,    nullptr, nullptr, USART3, nullptr },
+#endif
           { -1, NC, },
               }},
           aux_options,