add err & sol

.gitignore

@@ -0,0 +1,2 @@
+#gitbook files
+_book/

QA.md

@@ -1,2 +0,0 @@
-## Q&A
-

README.md

@@ -1,4 +1,7 @@
 # Introduction
 
 ## FPGA OL
-**FPGA Online(FPGAOL)** aims at offering online FPGA development board for cs courses and experiments. The FPGA DEV board is easily accessible through a browser. Human interface including LEDs and switches on web pages is available. Also, sample-based waveform charts help with development and debugging.
+
+![LOGO](img/logo.png)
+
+**FPGA Online(FPGAOL)** aims at offering online FPGA development board for cs courses and experiments. The FPGA DEV board is easily accessible through a browser. Human interface including LEDs and switches on web pages is available. Also, sample-based waveform charts help with development and debugging.

SUMMARY.md

@@ -4,4 +4,4 @@
 * [User Guide](user_guide/README.md)
     * [Developing FPGA Projects](user_guide/ch1.md)
     * [Testing your Design on FPGAOL](user_guide/ch2.md)
-* [Q&A](QA.md)
+* [Error&solution](err_sol.md)

err_sol.md

@@ -0,0 +1,109 @@
+## Error and Solution
+
+### can not login
+
+Error message:
+
+```
+Your username and password didn't match.
+Please try again.
+```
+
+Possible reason:
+
+* wrong username or password
+
+Solution:
+
+Check your username and password. Or Ask the administrator to reset your password.
+
+### refuse to acquire
+
+Error message:
+
+```
+Sorry, but...
+You might see this page if you:
+......
+WARNING: This will release the FPGA you are currently using.
+```
+
+Possible reason:
+
+* Attemptted to acquire multiple FPGA instances.
+* Opened two FPGA pages.
+* Refreshed the FPGA page.
+
+Solution:
+
+Open only one FPGA page. Or press **Reacquire** button.
+
+### no instance available
+
+Error message:
+
+```
+There are no FPGA instances currently available.
+```
+
+Possible reason:
+
+* Some devices were accidentally offline.
+* Many users are using at the same time.
+* Both above.
+
+Solution:
+
+Wait and try again. Or contact with the administrator.
+
+### upload or program fail
+
+Error message:
+
+```
+Failed to program device with the uploaded file. Perhaps this file is not a valid bitstream?
+```
+
+Possible reason:
+
+* You have select the wrong chip(not **xc7a100tcsg324-1**).
+* poor network condition.
+* Some device(s) accidentally went wrong.
+
+Solution:
+
+Check the chip you select and try again.
+
+### connection closed
+
+Error message:
+
+```
+Connection closed unexpectedly!
+Perhaps it's a network error
+or you may be holding FPGA for too long (>10 min).
+```
+
+Possible reason:
+
+* poor network condition.
+* timeout.
+
+Solution:
+
+Wait and try again.
+
+### fail to render waveform
+
+No Error message:
+(your browser get stuck)
+
+Possible reason:
+
+* The signal you put on LED(s) change too rapidly.
+* poor network condition.
+
+Solution:
+
+Use **period** mode waveform.
+