Regarding GPIO Feature

[mikemanzano.javier9]

Posted on November 23, 2014 at 14:05

Hi, Ive been using several MCU before. Its my first time to use STMicro.

Now Im currently studying its architecture.

My question is, what is the use of GPIO BSRR (Bit Set Reset Register) when we can access or write each bit with GPIO ODR (Output Data Register)?

We can use Bitwise Or and Bitwise and to write each bit right?

We can also bit banding for the same function right?

I am curious if there is a special application where we can take advantage of this register.

For now, i only see it as redundancy. 

Please help me understand the product.

Thanks,

Best Regards,

Michael Javier

#stm32-gpio-architecture

[Tesla DeLorean]

Posted on November 23, 2014 at 15:08

On the ARM architecture Loading and Storing aren't particularly rapid, doing a RMW* operation will take at least three instructions, four if the address needs loading. Peripheral registers are ''volatile'' so must be read each time they are used, the compiler can't cache them in processor registers.

Peripheral registers are not like regular memory.

You can write the GPIO latches directly via ODR. If you want to set specific bits high or low, and don't know the current state of them, using BSRR allows you to set and reset multiple bits, in a single atomic write which modifies the GPIO latches in one action. A write to BSRR is like a RMW on ODR, done at a hardware level.

*RMW - Read Modify Write

ODR &= ~1;

ODR |= 2;

ODR ^= 5;

Bit banding isn't particularly effective either, and has hazards on the TIM

[mikemanzano.javier9]

Posted on August 15, 2015 at 02:58

Good Day!

thanks for the reply. I got better understanding of the product through that.

Next is a different topic,  im posting my question here because I can find how to add new thread on e2e, so

I have STM32F Discovery and it was working fine with IAR. Then I used it as training materials to trainee of our company.

Without my knowledge, the trainee search on net how to use it, and used it with visual studio (STM32F4-Discovery tutorial with Visual Studio - VisualGDB).

Then she was not able to control it and when I tried to switch back to IAR, the built in STLink cannot find the MCU anymore.

I like to seek help regarding this. 

Thank in advance.

Mike Javier

[Tesla DeLorean]

Posted on August 15, 2015 at 03:18

If it's a problem with other code loaded on the board you can strap BOOT(0) pin to VDD, then reset, try to connect and erase like that.

Alternately you can see if you have a ''Connect Under Reset'' option, either in IAR, or through the ST-LINK Utilities.

Starting new threads, click ''New'' in top left immediately above the list of posts.

[Tesla DeLorean]

Posted on August 15, 2015 at 03:22

[mikemanzano.javier9]

Posted on August 16, 2015 at 08:33

Thanks for the fast support.

I tried the option 2 first and, that is to use the option connect during reset, but another error output as follow:

Sun Aug 16, 2015 14:07:40: Loaded macro file: C:\Program Files (x86)\IAR Systems\Embedded Workbench 6.5\arm\config\flashloader\ST\FlashSTM32F4xxx.mac 

Sun Aug 16, 2015 14:07:40: Selecting SWD as current target interface. 

Sun Aug 16, 2015 14:07:40: Hardware reset with strategy 2 was performed 

Sun Aug 16, 2015 14:07:40: Initial reset was performed 

Sun Aug 16, 2015 14:07:41: 736 bytes downloaded and verified (3.84 Kbytes/sec) 

Sun Aug 16, 2015 14:07:41: Warning: Verify error, failed to read memory at address 0x20000000 - 0x2000001F 

Sun Aug 16, 2015 14:07:41: Warning:  

Verify error at address 0x20000000, target byte: 0x16, byte in file: 0x00 

Sun Aug 16, 2015 14:07:41: Warning:  

Verify error at address 0x20000002, target byte: 0x00, byte in file: 0x02 

Sun Aug 16, 2015 14:07:41: Warning:  

Verify error at address 0x20000003, target byte: 0x00, byte in file: 0x20 

Sun Aug 16, 2015 14:07:41: Warning:  

Verify error at address 0x20000004, target byte: 0x16, byte in file: 0x05 

... and so on ...

Sun Aug 16, 2015 14:07:41: Warning: Too many verify errors, only the first 200 are displayed 

Sun Aug 16, 2015 14:07:57: Fatal error: There were warnings during download of FLASH loader, see Log Window   Session aborted! 

Sun Aug 16, 2015 14:07:57: Failed to load flash loader: C:\Program Files (x86)\IAR Systems\Embedded Workbench 6.5\arm\config\flashloader\ST\FlashSTM32F4xxx.out 

Sun Aug 16, 2015 14:07:57: Failed to load flash loader: C:\Program Files (x86)\IAR Systems\Embedded Workbench 6.5\arm\config\flashloader\ST\FlashSTM32F4xxx.flash 

For the first method, my undeerstunding is I have to desolder SB18 so that BOOT0 will be pull up instead of pulldown. I havent yet tried this, I will try it tomorrow when I get to the lab. 

Thanks.

Best Regards,

Michael Javier

[mikemanzano.javier9]

Posted on August 18, 2015 at 04:39

Hi Clive,

I already tried the option 1 that is to connect boot 0 to VDD, and it woks!

Thank you very much.