探讨STM32ISP及STM32波特率自动识别技术(菜农)
Jul 13th, 2008 | By hotpower | Category: ARM园地探讨STM32ISP及STM32波特率自动识别技术(菜农)
STM32之ISP也同其他ISP一样采用从机(STM32)波特率自动识别技术.
它采用非常“不理智”的偶校验(一个字节前面加一位校验位使得“1”的个数保持为偶数)，菜农对其不
慎满意~~~
为什么？？？…(俺不说)
识别码0×7F，即S 1111 1110 P T (其中S为起始位,P为校验位,T为停止位)
或： 0 1111 1110 1 1
可以“看出”它采用“7:1”识别模式。
即D0D1D2D3D4D5D6的脉宽是S脉宽的7倍.
或D0D1D2D3D4D5D6的脉宽是D7脉宽的7倍.
波特率自动识别技术有很多种，其中最常见的是定长对变长波特率自动识别技术
STM32的波特率自动识别技术为PC端为定长波特率(可变化但波特率保证正确)
STM32侧由于事先不知主机(PC)的波特率大小, 故其必须测量PC的波特率信号脉宽。
从机测量波特率信号脉宽也有多种，最常见的也是最蠢笨的脉宽测量.
从前面所述“7:1”识别模式可以看出:
主机发送识别码0×7f后，从机侧的S被拉低为0，故可对STM32产生中断，即同步开始。
但由于中断要占用MCU的中断向量表部分,故ISP程序为不影响用户的
代码空间一般采用IO查询+定时计数模式.
STM32的大鼻子老外的脑浆也是白色的，故跑不出此套路~~~如同NXP等~~~
菜农的脑浆是”红色”的~~~故肯定不会采用此“低级趣味”的方法~~~
让俺会这样定义（设计）:
1.主机以某一固定波特率表中正确的波特率间隔循环发送识别码0×7f.
2.从机（假设主频已漂移）先用正常主频的波特率表中循环取出正确的波特率并
间隔地从硬件端口读取接收的数据直到接收到识别码0×7f为止。
若主频未漂移，那么循环表中所有波特率必然收到识别码0×7f,自适应过程结束.
否则,上下微调波特率表中的所有时间常数则最后必然找到识别码0×7f.
菜农在GPS上就采用这种波特率自动识别技术，因为GPS模块是以某一固定的波特率
“没命的发送NEMA0813语句”，这就满足了“主机循环发送识别码”的协定。
波特率自适应就说完了~~~开始分析STM32的自动ISP过程吧~~~
首先ISP必须要有个进入开关设定,即Boot1/Boot0的设置.
我们可以简化为Boot1恒为1，Boot0为进入开关.
STM32的Boot0为: 1—运行状态 0—ISP状态
激活ISP状态由Reset信号完成，这样就保证了在任意时刻只能在一种条件下工作的约定(公理)
所以我们只需控制好Boot0和Reset这2个信号即可实现自动ISP~~~
有很多人不满菜农的自动ISP行为~~~谁让俺学的是自控呢???
N十年前俺在农校的第1堂课在笔记本上写的第1行字(可能也是当时的革命誓言吧):
让人类从繁重地危害身心健康的体力劳动中解放出来!!!
多年来俺一直想着这个“誓言”和“梦想”~~~从不违犯~~~所以俺设计的产品可以“笑傲江湖”十数年~~~
言归正传.试想一下：
当产品完成设计交付用户时，机壳肯定是封死的，除非是开发板之类的俺无话可说~~~
但是搞产品要想“笑傲江湖”十数年就必须考虑任何微小的细节。
现在是网络时代，USB转串口技术的成熟使都认为的工控通讯用串口是小儿科的歪论破灭！！！
可以看到各厂家对串口的重新定位，特别是多串口产品,像ST就比较“超前”~~~
随着技术的进步和用户的需求，远程诊断和ISP肯定是个方向.
自动ISP可以解决不愿给源码又不愿付差旅费的烦恼，而且也从ISP软件升级后延长产品的寿命.
ISP过程实际就是发送接收方各自的攻防体系的建立和实现过程:
主机发送信号,从机接收信号并应答，反之亦然.
小朋友和网友说ST的ISP有时很难联机通讯,俺开始玩STM32时也觉得如此，后来还好些。
主要是菜农近来的打击目标侧重在DSP上，就一直没追究其问题的所在.
不过对STMISP软件未带自动ISP很是不满~~~所以当菜鸟时就与香主“盲谈”了自动ISP的构建.
俺有个不好的习惯~~~ 一但俺认证可行后，只要不搞产品就不会去急迫地实施—虽然可行…
小朋友说网友说俺忽悠人~~~冤枉菜农了~~~
因为俺无法抽身~~~俺不愿放过用HotBios叫板TI的DSP/BIOS的大好机会~~~
HotComm是菜农三剑客之一,俺存放了一年一直舍不得就压在了“箱底”不愿见阳光~~~
因为它设计的目标就是倒塌地球上一切的串口控件~~~
这次HotComm要为俺在STM32上的“忽悠”赎罪卖身了~~~心痛+悲痛之中…
(可能有些人会说菜农太狂妄~~~正如VxWorks专家吴旭光教授说俺颠覆OS理论太狂一样~~~有空
他要到他那里去切磋~~~)
又跑题了~~~
仔细分析STM32ISP的数据流向，可以找到很规律的关系。
不外乎你攻我守，你守我攻。
但如果攻守失衡，必然带来死机的结果~~~
现在做到的是如何解脱死机（死锁）???—只有Reset!!!
现在看到自动ISP的好处和威力了吧—不怕死，就怕死了救不活!!!
(小朋友名句—功夫在高，也怕菜刀)菜农想做到—菜刀砍过，人鬼不倒~~~才是高~~~
自动ISP电路很简单，俺和小朋友先在EK…忘了板名和厂家了~~~就是那个199的~~~
LPCARM采用DTR->Reset,RTS->ISP. 所以俺就抄袭这个习俗吧~~~但愿NXP的大鼻子别告俺~~~
由于DTR/RTS是232电平，即-15V~+15V, 一般在+-10V左右。
一般采用RS232芯片实现232/TTL电平转换，也可用二极管、三极管
但要注意电平的钳位及限流问题。
RS232内部有2入2出。
而作为主机,信号方向有3出1入.
即TX(STM32的RXD),DTR(RST),RTS(BOOT0)为输出信号, RX(STM32的TXD)为输入信号.
RS232芯片一般只连接RXD/TXD这2个信号，故还剩1入1出未用.
将DTR接入RS232电平转换芯片,那么STM32的RST就得到了正常的电平控制。
考虑硬件存在线与问题，故：RS232的TTL输出加一只二极管D1到RST.
再考虑Boot0的连接问题：
由于RTS是232的+-10V,那么肯定不能直接和Boot0连接。
由于Boot0我们可以把它结果100K电阻(厂家标注)上拉至VCC.（STM32的运行状态）
所以我们只需在Boot0上施加低电平即可设定ISP模式.
故可用二极管D2单向取-10V即可，考虑STM32不能承受负电压，故可在接二极管D3到地GND(VSS)
来将RTS钳位在-0.7V.
由于D3的钳位导致了RTS信号过流，故必须用串接10K左右的电阻R1来限流。
到此自动ISP硬件电路的改造过程以付出D1,D2,D3和R1的“代价”轻松搞定~~~
若搞产品可继续：在Boot0端再串接二极管D4来消除D3钳位造成的负压-0.7V.
在Boot0,RST上各接102(或103，104)电容防止信号误触发.
自动ISP硬件“电路图”如下:
+–>VCC
100K(板子自带)
|
(负极) (正极) |
RTS—->–R1–> -D2+ ——-+– (-D4+)–+–> STM32_Boot0 (注D4可不接,短路或加电阻即可)
(DB7) |
-(负极)
D3
+(正极)
|
=
GND
(DB4) (负极) (正极)
DTR—->–RS232————> -D1+ –>STM32_RST
(232入) (TTL出)
一般DTR/RTS未接PC时都为-10V左右,所以拔掉也不能影响STM32的
正常工作.
由于RS232内部实际为反向器，故:
DTR = -10V时RS232输出高电平到RST，即STM32正常运行状态.
RTS = -10V时经过二极管的单向导电特性，Boot0为0进入ISP状态.
但是注意: 如果PC未介入,RTS上不会有电压信号,故Boot0依然为1
所以RTS的工作重点只是如何拉低Boot0上的电压!!!
若无PC谈何拉低Boot0???
所以PC脱机后该电路也不会影响STM32的原工作状态的~~~
相反PC ISP完成后(假使还在ISP状态)再脱机，STM32会自动回到运行状态~~~
这—–就是自动ISP的”真谛”所在~~~
菜农HotPower@126.com 2008.7.13 11:30 于雁塔菜地
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菜农，这里有错误？
应用笔记：AN2606 STM32F101xx and STM32F103xx system memory boot mode 第5页
在复位时当BOOT0=0进入用正常工作模式，
当BOOT0=1进入ISP模式。
菜农的自动ISP硬件“电路图”：
+–>VCC
100K(板子自带)
|
(负极) (正极) |
RTS—->–R1–> -D2+ ——-+– (-D4+)–+–> STM32_Boot0 (注D4可不接,短路或加电阻即可)
(DB7) |
-(负极)
D3
+(正极)
|
=
GND
(DB4) (负极) (正极)
DTR—->–RS232————> -D1+ –>STM32_RST
(232入) (TTL出)
在连PC时，因为PC串口的DTR/RTS输出为-10V，由于RS232内部为反向器，故：
DTR = -10V时RS232输出高电平到RST，即STM32正常运行状态.
RTS = -10V时经过二极管的单向导电特性，Boot0为0进入User Flash Memory.
但是注意： 如果PC的ISP软件未介入，故Boot0依然为0.
当执行ISP软件后才能让DTR = +10V，RS232输出低电平到RST，即使STM32复位，
RTS = +10V时经过二极管的单向导电特性，Boot0为1进入System Memory，
这样可以进行ISP写入程序。
在未连PC时：
DTR未接入，但RS232输出依然是高电平到RST，即STM32正常运行状态.
RTS 未接入，Boot0为1进入System Memory.
注意：因为Boot0为1进入System Memory，所以STM复位后不能进入正常工作状态。
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