doc: add link http://elm-chan.org/ to linkcheck_ignore

Signed-off-by: Jingru <[email protected]>

Author: wangnuannuan

doc/documents/conf.py

@@ -182,7 +182,8 @@
 intersphinx_mapping = {'https://docs.python.org/': None}
 
 linkcheck_ignore = [
-    'http://www.solomon-systech.com/en/product/display-ic/oled-driver-controller/ssd1306/', 
+    'http://www.solomon-systech.com/en/product/display-ic/oled-driver-controller/ssd1306/',
+    'http://elm-chan.org/', 
 ]
 
 rst_epilog =  u"""

doc/documents/getting_started/peripheral_preparation.rst

@@ -77,4 +77,4 @@ Driver code at ``embarc_osp/device/peripheral/adc/ad7991``.
 `ESP01\/ESP01S <https://wiki.ai-thinker.com/esp8266/docs>`_ : Primary IC type is ESP8266, use **UART** interface for data changing and controlling.
 Driver code at ``embarc_osp/device/peripheral/wifi/slip_esp``.
 
-The ESP01/ESP01S module is not originally a PMOD module, however it is PMOD compatible, meaning that you can wire it to PMOD interface on board. You need to connect GND(embARC) to GND(ESP) , 3.3V(embARC) to VCC(ESP), RXD(embARC) to TXD(ESP), and TXD(embARC) to RXD(ESP), respectively. Please take reference from datasheet of `ESP01\/ESP01S <http://wiki.ai-thinker.com/esp8266/docs>`_ and UART (type 4A) part of `Digilent Pmod Spec <https://www.digilentinc.com/Pmods/Digilent-Pmod_%20Interface_Specification.pdf>`_ for pin layout. 
+The ESP01/ESP01S module is not originally a PMOD module, however it is PMOD compatible, meaning that you can wire it to PMOD interface on board. You need to connect GND(embARC) to GND(ESP) , 3.3V(embARC) to VCC(ESP), RXD(embARC) to TXD(ESP), and TXD(embARC) to RXD(ESP), respectively. Please take reference from datasheet of `ESP01\/ESP01S <https://wiki.ai-thinker.com/esp8266/docs>`_ and UART (type 4A) part of `Digilent Pmod Spec <https://www.digilentinc.com/Pmods/Digilent-Pmod_%20Interface_Specification.pdf>`_ for pin layout.