LDmicro Forum - How to disable JTAG interface on Bluepill using LDmicro32 V6

How to disable JTAG interface on Bluepill using LDmicro32 V6 (by Ziggy)

Hello forum,

I have just hit the wall built by my ignorance.
I wished to get familiar with LDmicro32 and Blue pill micro controller ( STM32f103 ).
I happily went about designing a board for a task based completely oblivious of the fact the JTAG interface is enabled by default.
I am aware it can be switched off and THEN AND ONLY THEN can these pins be used as standard IO pins.
Readily achieved in C.
Is there a way of doing it in LDmicro32?
Earlier versions allowed register access from within LDmicro directly.
So now I have a PCB with disfunctional pin assignment. Sdly it is also populated.

Fri May 30 2025, 01:39:50

A solution in C (by Ziggy)

A way of disabling JTAG in C is to use the following statement in initialization code, disable JTAG (keep SWD if needed):

RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;
AFIO->MAPR |= AFIO_MAPR_SWJ_CFG_JTAGDISABLE;

This keeps SWD active for programming, but frees up PA15, PB3, PB4.
Would like to understand if LDmicro32 supports this kind of functionality natively?

Fri May 30 2025, 20:47:50

What it looks like (by Ziggy)

The additional instructions should be located in void PlcInit function

as a sample UNMODIFIED PlcInit function

// PLC ports and peripheral init
void PlcInit(void)
{
Gpio_conf('A', 0x8000, MODE_OUT);
Gpio_resetoutputs('A', 0x8000);
Gpio_conf('A', 0x7FFF, MODE_INP);
Gpio_conf('B', 0x4000, MODE_OUT);
Gpio_resetoutputs('B', 0x4000);
Gpio_conf('B', 0xBFFF, MODE_INP);
Gpio_conf('C', 0xFFFF, MODE_INP);

LibTimer_Init(TIM3, 1000, 720);
LibTimer_Interrupts(TIM3, ENABLE);
NVIC_SetPriority(TIM3_IRQn, 0);

}

And now a modified PlcInit function
Note location and content of additional JPEG disable lines

// PLC ports and peripheral init
void PlcInit(void)
{
// Enable clock to AFIO
RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;

// Disable JTAG, keep SWD active
AFIO->MAPR |= AFIO_MAPR_SWJ_CFG_JTAGDISABLE;

Gpio_conf('A', 0x8000, MODE_OUT);
Gpio_resetoutputs('A', 0x8000);
Gpio_conf('A', 0x7FFF, MODE_INP);
Gpio_conf('B', 0x4000, MODE_OUT);
Gpio_resetoutputs('B', 0x4000);
Gpio_conf('B', 0xBFFF, MODE_INP);
Gpio_conf('C', 0xFFFF, MODE_INP);

LibTimer_Init(TIM3, 1000, 720);
LibTimer_Interrupts(TIM3, ENABLE);
NVIC_SetPriority(TIM3_IRQn, 0);

}

I hope someone finds this of use. Please note the original PlcInit () function is created by LDmicro32.

Thu Jun 5 2025, 00:38:21

(no subject) (by José)

Hi Ziggy

That's fine ; you put questions and answer by yourself !

If your instructions:

RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;
AFIO->MAPR |= AFIO_MAPR_SWJ_CFG_JTAGDISABLE;

are supported by ARMGCC you can use them.

A better way to implement it would just be to add a function
in a library, for instance original Lib_gpio.h / .c as it frees some GPIO pins, in Libraries/Arm/STM32F1:

void LibGPIO_Disable_Jtag()
{
RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;
AFIO->MAPR |= AFIO_MAPR_SWJ_CFG_JTAGDISABLE;
}

Then, you edit the original file Input/plcbase_arm32.c
to add the instruction like that in PlcInit():

void PlcInit(void)
{
LibGPIO_Disable_Jtag();

#insert 1,plcinit.c $
#insert 1,plcdevinit.c $
}

So that the modification is automatical for any new project.

Could you try it and let us know if it works ?

BR
José

Thu Jun 5 2025, 09:45:09

(no subject) (by Ziggy)

Hello Jose,

Thank You for the suggestion.

So far i have stuck with the more manual copy paste

void PlcInit(void)
{
// Enable clock to AFIO
RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;

// Disable JTAG, keep SWD active
AFIO->MAPR |= AFIO_MAPR_SWJ_CFG_JTAGDISABLE;

Gpio_conf('A', 0x8000, MODE_OUT);

...
}

It is working for me and the code is doing what I want it to do...
however the response is SLOOOOOOOOWWWW.
I need to figure out why the micro runing at 72MHz does not produce a quick enough four digit, seven segment LED display.

It is next to useless.

Is there a configuration of IO PIN drivers which which would offer faster response?

Sat Jun 7 2025, 00:57:12