最近研究ST芯片的内容ISP升级方法，按照官方推荐方式，需要设置BOOT引脚电平进入内容System Bootloader升级，感觉这种方式麻烦，所以查找是否可以软件方式直接跳转ISP进行升级；经过百度和各论坛查找资料，终于找到解决办法，并且经过验证大部分是可行的，少部分不行(暂时还没有搞清楚原因)
. I! U  S* ~. F  H9 Z4 K4 M0 x; d  ^7 B以下是软件跳转内容ISP的代码，可以直接调用即可：
/**
* Function to perform jump to system memory boot from user application
*
* Call function when you want to jump to system memory
*/
1 X" E5 M! j% g- kvoid JumpToBootloader(void) {
        void (*SysMemBootJump)(void);
9 j! r* x) L# ^: h       
; S- s# d; h: {$ A7 a8 w        /**
         * Step: Set system memory address.
8 _1 _$ {4 h% V$ ^4 E( J, S         *      
         *       For STM32F429, system memory is on 0x1FFF 0000
& z5 y2 [* w5 ~. p; p# F/ m         *       For other families, check AN2606 document table 110 with descriptions of memory addresses
3 C8 O; p. j6 D& O- K! p3 z         */
        //volatile uint32_t addr = 0x1FFF0000;
    /**
         * Step: Set system memory address.
         *      
         *       For STM32F103, system memory is on 0x1FFF F000
         *       For other families, check AN2606 document table 110 with descriptions of memory addresses
         */
2 V3 D3 B5 U) H        //volatile uint32_t addr = 0x1FFFF000;
, ]* e' O: l: y3 P. C& P; v    /**
         * Step: Set system memory address.
* n- r& j- k& b1 Y' H# I  ?         *      
  a$ Z' z2 @3 y* S         *       For STM32F107, system memory is on 0x1FFF B000
6 F/ E* q0 Z" V7 s2 i3 B' d         *       For other families, check AN2606 document table 110 with descriptions of memory addresses
( ^  i3 |0 I* A/ h6 m         */
        //volatile uint32_t addr = 0x1FFFB000;
) F5 [5 b- D0 z, T: W, v    /**
: R7 {8 P; N' w         * Step: Set system memory address.
1 X6 }  ?4 L4 L2 P         *      
         *       For STM32F303, system memory is on 0x1FFF D800
, ~2 G' k+ n& S! D5 R         *       For other families, check AN2606 document table 110 with descriptions of memory addresses
         */
        //volatile uint32_t addr = 0x1FFFD800;
$ A0 V% O) f2 m  W3 D  ?        /**
         * Step: Set system memory address.
         *      
5 f0 j% L& x. x% k         *       For STM32L073, system memory is on 0x1FF0 0000
         *       For other families, check AN2606 document table 110 with descriptions of memory addresses
         */
        volatile uint32_t addr = 0x1FF00000;
$ E( U) l" X0 {, ?  i! C4 [: W& i& C       
        /**
% l5 I. K$ c, D6 O         * Step: Disable RCC, set it to default (after reset) settings
         *       Internal clock, no PLL, etc.
         */
#if defined(USE_HAL_DRIVER)
        HAL_RCC_DeInit();
#endif /* defined(USE_HAL_DRIVER) */
#if defined(USE_FULL_LL_DRIVER)
        LL_RCC_DeInit();
#endif
#if defined(USE_STDPERIPH_DRIVER)
; W& |% Z9 o0 D4 J* E5 u; V' c; _        RCC_DeInit();
#endif /* defined(USE_STDPERIPH_DRIVER) */
* c6 P0 u7 k/ l* c/ o3 U* g       
        /**
+ x6 e8 s3 a% g) f" H' Z         * Step: Disable systick timer and reset it to default values
         */
. Q) c7 N) x: R2 S2 b6 R1 U        SysTick->CTRL = 0;
* k1 g3 c) o" m6 G        SysTick->LOAD = 0;
        SysTick->VAL = 0;

        /**
         * Step: Disable all interrupts
         */
        __disable_irq();
       
/ X& k6 a3 n5 V3 A8 j! F9 D        /**
         * Step: Remap system memory to address 0x0000 0000 in address space
, d& s' K. {/ u5 ~/ x0 h) Q         *       For each family registers may be different.
         *       Check reference manual for each family.
         *
         *       For STM32F4xx, MEMRMP register in SYSCFG is used (bits[1:0])
         *       For STM32F0xx, CFGR1 register in SYSCFG is used (bits[1:0])
         *       For others, check family reference manual
         */
  |4 y8 u: `% u0 }+ f% R( T        //Remap by hand... {
( P# _* B+ b. ]' e( D6 w#if defined(STM32F4)
2 X: E" K9 p) \/ e3 c( k2 V. }        SYSCFG->MEMRMP = 0x01;
#endif
#if defined(STM32L0)
" I$ y! j. s2 P- Q+ p; S7 F6 D+ `3 P        SYSCFG->CFGR1 = 0x01;
#endif
3 R2 L- s+ K; y/ p- z* d7 z4 q#if defined(STM32F0)
; j0 s+ o4 w( f. R$ H! s) W        SYSCFG->CFGR1 = 0x01;
. u1 X: c5 j  X: O" I#endif
        //} ...or if you use HAL drivers
        //__HAL_SYSCFG_REMAPMEMORY_SYSTEMFLASH();        //Call HAL macro to do this for you
; A, ^3 z! f$ H+ ?  U       
        /**
7 y3 u8 P2 f' [* v- L3 i         * Step: Set jump memory location for system memory
! ?* _, z3 R+ L  ?         *       Use address with 4 bytes offset which specifies jump location where program starts
6 }6 z$ m3 M: U# m0 I         */
        SysMemBootJump = (void (*)(void)) (*((uint32_t *)(addr + 4)));
& S) ], ~6 }/ a+ k" j) [5 M       
        /**
         * Step: Set main stack pointer.
" ^8 E, ?& ~' _+ i; a         *       This step must be done last otherwise local variables in this function
. R/ _2 D3 Z, z         *       don't have proper value since stack pointer is located on different position
         *
         *       Set direct address location which specifies stack pointer in SRAM location
. w6 C  D3 C- s; L: t4 r3 L         */
        __set_MSP(*(uint32_t *)addr);
' Q" t) {2 y9 V8 ]. ?; f       
        /**
/ ?  l5 f* R* P         * Step: Actually call our function to jump to set location
         *       This will start system memory execution
6 b) N7 @3 n; `: l         */
        SysMemBootJump();
       
        /**
$ b# o- s( X3 C# h, s& ]         * Step: Connect USB<->UART converter to dedicated USART pins and test
         *       and test with bootloader works with STM32 Flash Loader Demonstrator software
         */
}
然后介绍下测试结果：
% B2 e1 {1 @' [! N( z" o1、F0系列：STM32F030、STM32F051、STM32F070、STM32F071和STM32F072芯片，其中除STM32F070跳转运行ISP运行错误(发现内部ISP代码好像有问题，具体也不确定)外，均可以支持软件跳转ISP后串口方式升级；
2 `4 C! z0 i1 c  I: _  f/ j2 H5 a9 Y2、F1系列：STM32F103和STM32F107芯片，均可以支持软件跳转ISP后串口方式升级；
3、F2系列：无芯片平台验证；
4、F4系列：STM32F407芯片，支持软件跳转ISP后串口方式升级；
5、L0系列：STM32L073芯片，支持软件跳转ISP后串口方式升级；
6、L4系列：STM32L4R5芯片，软件跳转ISP后运行直接跳转Hardfault(后续查找原因)；
7、其它系列均无平台验证；
8 I  Z# K4 T" }: t

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请问你一下，SMT32L4R5ZIT6如何进入system bootloader？这个芯片只有BOOT0，在官网提供的开发板上，无论是置高还是置低，用那个demonstrator工具，也不能进行升级呢。
我用的开发板是官方的nucleo开发板，连接串口用的是lpuart1