Simultaneous FSMC usage on STM32F2

[jon239955_stm1_st]

Posted on July 18, 2016 at 09:49

I am using an STM32F2 MCU and currently successfully executing code from external SRAM on FSMC Bank 1, NOR/PSRAM 1.

What I would like to do is also use the LCD on Bank 1, NOR/PSRAM 2 while executing from this external SRAM.

I have made the assumption that this is not possible simultaneously and would like verification of that?

Along these lines anyway, I have specifically placed any module that accesses the FSMC for the LCD into internal SRAM so that it is not executing instructions over the FSMC while trying to access the LCD but this hasn't worked.

I know the LCD works because the same code running exclusively from internal SRAM works OK.

Any thoughts?

#lcd #stm32f2 #fsmc

[waclawek.jan]

Posted on July 19, 2016 at 16:10

Well, for example, if  the LCD's chipselect is stuck to an always-active level, it would work when nothing else is on the bus, but writes to RAM would go simultaneously to the LCD, possibly knocking it off.

I can imagine also more subtle timing-related issues, too.

Time for oscilloscope.

JW

[jon239955_stm1_st]

Posted on July 19, 2016 at 16:25

It's not a chip select issue.  This code is a test sample but the same display in ''proper'' code successfully uses the FSMC for external SRAM for heap storage as well as driving the LCD at the same time. If writes to external SRAM were also targeting the LCD, we would see that corruption, no?

Is there anything specifically that I should look for with regards to timing?  What exactly might be the problem?  Time between de-assertion of SRAM and moving to assertion of LCD?  I could test this by having delays before any LCD accesses?

[waclawek.jan]

Posted on July 19, 2016 at 17:45

> It's not a chip select issue. 

It was an example.

What did the oscilloscope say?

JW