下载程序时提示：Error: Flash Download failed  -  "Cortex-M4"
具体的信息如下

JLink info:
------------
DLL: V4.94j, compiled Dec 10 2014 13:52:41
Firmware: J-Link ARM V8 compiled Nov 28 2014 13:44:46
Hardware: V8.00
S/N : 163....
Feature(s) : RDI,FlashDL,FlashBP,JFlash,GDBFULL 
 
* JLink Info: TotalIRLen = 9, IRPrint = 0x0011
* JLink Info: TotalIRLen = 9, IRPrint = 0x0011
* JLink Info: Found Cortex-M4 r0p1, Little endian.
* JLink Info: FPUnit: 6 code (BP) slots and 2 literal slots
* JLink Info: TPIU fitted.
* JLink Info: ETM fitted.
ROMTableAddr = 0xE00FF003
**JLink Warning: Could not set S_RESET_ST
**JLink Warning: Could not set S_RESET_ST
 
Target info:
------------
Device: STM32F407VG
VTarget = 2.018V
State of Pins: 
TCK: 1, TDI: 0, TDO: 1, TMS: 0, TRES: 0, TRST: 1
Hardware-Breakpoints: 6
Software-Breakpoints: 8192
Watchpoints:          4
JTAG speed: 3000 kHz
 
Erase Failed!
Error: Flash Download failed  -  "Cortex-M4"
Flash Load finished at 15:24:32


有两个疑问：
1 **JLink Warning: Could not set S_RESET_ST，这个警告是什么意思
2 VTarget = 2.018V，这个电压是什么电压，我测量Jtag引脚的电压是3.2v，板子的电压是5V