1. I am using STM32F205, with serial wire debug, composing reset, clk, data & gnd pins. 2. Whenever I connect debugger my code runs perfectly. But without debugger, sometimes code just don't run. I am toggling a pin which never happens. it happens only sometimes. 3. No other clk init is done, so default 16Mhz clck, as soon as MCU power up, I keep on toggling pin. No code in between so couldn't be memory access other or anything. So pin toggle. 3. I have 0.1uf cap on reset pin & 10k pull down on boot pins. 4. However I have left swclk & swdata pins float. 5. I had checked below link & connected 10k pull down to clk & 10k pull-up to data. support.code-red-tech.com/.../HardwareDebugConnections
6. I will check multiple times before reaching conclusion, but any idea on this.
A RC-driven reset pin is a well-known way to fail, since it will only manage a proper reset in some limited situations. After a short off-on of the power, the capacitor will be partially charged and give too short reset. And a short dip of the supply voltage will not be properly handled.
It's quite likely that the debug adapter solves your issue since it will take control of the reset signal.
Another thing - you should never leave input pins floating. If the datasheet doesn't clearly indicate that the chip has internal pull-up or pull-down, then you should supply external pull-up or pull-down. Lots of strange things can happen with floating inputs. You can get very high current consumption. And the input can function as a radio antenna, picking up noise from the air or from neighbour signals and feeding the chip with unexpected input signals.
1. Load is around 50mA. I have bypassed the supply properly & checked in CRO, till now no issues. 2. In reset network, R is internal to STM32F205 as datasheet mentions, I have only 0.1uF external capacitor to it. 3. I will make every unused pin as internal pull-up. 4. From yesterday, problem has arrived only once. When MCU failed to start. 5. When control enter inside the program, I toggle a pin at default clock. So that mean control never enter the main. I have disabled systeminit() code by pacing a return at first line. So when code enter main , only then i can make pins internal pull-up. 6. there is also 10K pull-down to boot0 pin so code should enter flash rather than RAM.
1. I had same problem in two boards. 2. In one of board, again same problem came, & I had noticed that reset pin is low (which is bypassed by 0.1uF). 3. I have checked all VDD & VSS pins on CRO, all are ok. 4. Additionally i had connected two 10pf caps on pins PH0-OSC_IN , PH1-OSC_OUT. However no oscillator is connected since i am using internal oscillator. They were soldered during soldering process at that I don't have oscillator. Right now i am using internal oscillator. 5. Pin sequence of MCU is: PH0-OSC_IN(5) , PH1-OSC_OUT(6) , & NRST(7) 6. however datsheet says on power up , oscillator pins are default to GPIO. 7. So could this be problem?
Edit: 8. Right now I have removed these caps, & board is working again. but I am not sure.
1. Again problem arises. I had checked that reset pin voltage output is low. Don't know why it so. So code never runs, as MCU is in rese state always.
What can lead to hardware reset pin to logic, provided there is only 0.1uF cap across it. & 0.1uF is of 16V.
2. I have changed that 0.1uF cap also, in 1 board problem gone, while in other problem still remains. I have checked that removed 0.1uF cap, it is showing correct value in DMM.
Why play with the capacitor? You don't get any time constant without it - and unless it leaks a lot or have infinite capacitance it can't block the reset line from going high if there is an internal or external pull-up that can charge the capacitor.
Is the supply voltage available on every single supply pin of the chip? And is the supply voltage above the configured Vpor/Vbor?
And if your chip has a IRROFF pin - what is the state? If available and connected to VDD, then you need an external supervisor chip.
And if your chip has a REGOFF pin - what is the state?
Have you walked through all chapters related to power modes and reset in the datasheet and verified all conditions?