Update flow control notes

Author: nseidle

README.md

@@ -5,13 +5,17 @@ SparkFun LoRaSerial
 
 [*SparkFun GPS-RTK-SMA - ZED-F9P (GPS-19311)*](https://www.sparkfun.com/products/19311)
 
+Head to the [LoRaSerial Product Manual](http://docs.sparkfun.com/SparkFun_LoRaSerial/intro/) for technical documentation.
+
 LoRaSerial is a pair of serial radio modems that simply passes serial back and forth. Do you have a system that needs to report data every few seconds? Is it located beyond WiFi or Bluetooth range? Do you need 9 mile/15 kilometer range? LoRaSerial transmits data over LoRa giving it incredible range compared to other methods. We’ve regularly transmitted over 9 miles/15km line-of-sight using two LoRaSerial radios, right out of the box.
 
-LoRaSerial utilizes a 1 watt 915MHz transceiver and an open source protocol to and transmit AES encrypted data at 4800bps or approximately 480 bytes per second. Video streaming, this is not. LoRaSerial is very good at getting whatever data you need from point A to point B, encrypted, without configuration. The radios automatically frequency hop (FHSS) between channels to avoid collisions. The ‘airspeed’ or data rate is configurable up to approximately 3,000 bytes per second for shorter range, or for *extremely* long range transmissions, as low as 4 bytes per second.
+LoRaSerial utilizes a 1 watt 915MHz transceiver and an open source protocol to and transmit AES encrypted data at 4800bps or approximately 480 bytes per second. Video streaming, this is not. LoRaSerial is very good at getting whatever data you need from point A to point B, encrypted, without configuration. The radios automatically frequency hop (FHSS) between channels to avoid collisions. The ‘airspeed’ or data rate is configurable up to approximately 2,000 bytes per second for shorter range, or for *extremely* long range transmissions, as low as 400 bytes per second.
+
 LoRaSerial radios support simple point to point and point as well as multipoint broadcasts. Multipoint broadcasting makes it ideal for GNSS RTK and many other scenarios where one device needs to produce data and many devices need to consume that data.
 
 The LoRaSerial firmware supports an innovative and simple to use ‘training’ method. Pressing the train button on both radios will generate a new random network ID and AES encryption key and share them between radios. This makes pairing radios in the field as simple as a button press. WiFi WPS this is not. Bring the radios near each other and the LoRaSerial training method is simple and secure.
-Currently SparkFun is offering radios utilizing 915MHz modems that are allowed in most parts of the world. Please check your local restrictions. The radios are fully configurable to restrict frequencies, channels, dwell time, power output, and a variety of other settings to make the radios compatible with your local regulations.
+
+Currently, SparkFun is offering radios utilizing 915MHz modems that are allowed in most parts of the world. Please check your local restrictions. The radios are fully configurable to restrict frequencies, channels, dwell time, power output, and a variety of other settings to make the radios compatible with your local regulations.
 
 Repository Contents
 -------------------
@@ -24,7 +28,7 @@ Repository Contents
 Documentation
 --------------
 
-* **[LoRaSerial Hookup Guide](https://learn.sparkfun.com/tutorials/loraserial-hookup-guide)** - Hookup guide for the SparkFun LoRaSerial.
+* **[LoRaSerial Product Manual](http://docs.sparkfun.com/SparkFun_LoRaSerial/intro/)** - Configuration guide for the SparkFun LoRaSerial.
 
 License Information
 -------------------

docs/hardware_overview.md

@@ -51,6 +51,19 @@ The pinout is as follows:
 
 **GND** (Ground) - Connect this pin to the ground of your system.
 
+#### Flow Control
+
+Hardware flow control applies to both the UART connection and the USB connector but in slightly different ways. 
+
+If Flow Control is enabled, the UART will use standard CTS and RTS pins to control the flow. If LoRaSerial is running low on serial buffer space, and Flow Control is enabled, it will pull RTS low to indicate to the host to refrain from sending data to LoRaSerial. 
+
+The USB connection uses a concept called backpressure. It is not affected by the [FlowControl setting](http://docs.sparkfun.com/SparkFun_LoRaSerial/at_commands/#serial-commands) and cannot be disabled. If LoRaSerial is not able to read the incoming data fast enough, the USB driver will indicate to the host’s operating system that the data has not been consumed. Depending on the application, data will either be paused or lost. 
+
+
+![STRSVR Buffering Serial Data](img/RTKLIB%20STRSVR%20Buffering%20Data.png)
+
+This is most obvious in applications such as STRSVR (from [RTKLIB](https://rtklib.com/)). If STRSVR sends more data to the LoRaSerial than it can consume, STRSVR will begin to buffer the data until it can be sent. This is problematic for time-sensitive data, such as RTCM, where data, being delivered successfully but delayed but multiple seconds, can cause problems with RTK. If RTCM data is multiple seconds old, an RTK Fix will go to RTK Float, then fail because current RTCM data is not being delivered to the far end of the radio link. The easiest way to fix the problem is to increase the AirSpeed of the link.
+
 ### RSSI LEDs
 
 ![4 LEDs indicating signal strength](Original/SparkFun_LoRaSerial_-_RSSI_LEDs.png)
@@ -109,7 +122,7 @@ Please see [Updating LoRaSerial Firmware](docs\firmware_update.md) for more info
 
 Two GPIOs capable of ADC are broken out for potential future use.
 
-### UFL Connector
+### U.FL Connector
 
 ![Zero ohm jumper resistor and U.FL connector](Original/SparkFun_LoRaSerial_-_1W_LoRa_Module_UFL.png)
 

docs/img/RTKLIB STRSVR Buffering Data.png

@@ -2,7 +2,7 @@
 
 Out of the box, the SparkFun LoRaSerial products are simple-to-use serial radios and can be used with little or no configuration. This Product Manual provides detailed descriptions of all the available features of the LoRaSerial products.
 
-The line of LoRaSerial products offered by SparkFun all run identical firmware. The [LoRaSerial](https://github.com/sparkfun/SparkFun_LoRaSerial) and this guide cover the following products:
+The line of LoRaSerial products offered by SparkFun all run identical firmware. The [LoRaSerial repo](https://github.com/sparkfun/SparkFun_LoRaSerial) and this guide cover the following products:
 
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