A20 User Manual (Revision 1.2) Copyright © 2013 Allwinner Technology Co., Ltd. All Rights Reserved. Page 95 / 812
1.6. System Boot
1.6.1. Overview
A20 supports system boot from NAND Flash, SPI NOR Flash (SPI0), SD card (SDC 0/2), and USB.
After power on, the system will try to boot from SDC0, NAND Flash, SDC2, SPI0, and USB
successively, but if the Boot Select Pin, or BSP, an external pin that is used to select system boot
method, is checked to be in low level state, the system will direclty boot from USB. In normal state,
this pin is pulled up by an internal 50K resistor.
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