在主程序里添加了这句;
systemPowerDown(SYS_SLEEP_MODE);
后，就不能下载程序了，提示如下
Dap: Error connecting to the target: (Error -1170 @ 0x0) Unable to access the DAP. Reset the device, and retry the operation. If error persists, confirm configuration, power-cycle the board, and/or try more reliable JTAG settings (e.g. lower TCLK). (Emulation package 7.0.100.0)