How can I use internal 64Kbytes SRAM ?

[antonius]

Posted on August 18, 2015 at 12:41

Guys,

How can I use internal 64Kbytes SRAM from STM32F107?

Any code example from StdPeripheral ?

Thanks

[mh.ferris9]

Posted on August 18, 2015 at 13:14

Any normal variable you declare will be stored in SRAM automatically.

This'll be in SRAM:

u8 myArray[256];  

Am I perhaps not understanding what you mean?

[antonius]

Posted on August 18, 2015 at 13:18

I see, thanks for responding...

how to implement this in code ?

I read from datasheet reference :

3.3.1 Embedded SRAM

 

The STM32F10xxx features up to 96 Kbytes of static SRAM. It can be accessed as bytes,

 

half-words (16 bits) or full words (32 bits). The SRAM start address is 0x2000 0000.

 

3.3.2 Bit banding

 

The Cortex®-M3 memory map includes two bit-band regions. These regions map each word

 

in an alias region of memory to a bit in a bit-band region of memory. Writing to a word in the

 

alias region has the same effect as a read-modify-write operation on the targeted bit in the

 

bit-band region.

 

In the STM32F10xxx both peripheral registers and SRAM are mapped in a bit-band region.

 

This allows single bit-band write and read operations to be performed. The operations are

 

only available for Cortex®-M3 accesses, not from other bus masters (e.g. DMA).

 

A mapping formula shows how to reference each word in the alias region to a corresponding

 

bit in the bit-band region. The mapping formula is:

 

bit_word_addr = bit_band_base + (byte_offset x 32) + (bit_number × 4)

 

where:

 

bit_word_addr is the address of the word in the alias memory region that maps to the

 

targeted bit.

 

bit_band_base is the starting address of the alias region

 

byte_offset is the number of the byte in the bit-band region that contains the targeted

 

bit

 

bit_number is the bit position (0-7) of the targeted bit.

 

Example:

 

The following example shows how to map bit 2 of the byte located at SRAM address

 

0x20000300 in the alias region:

 

0x22006008 = 0x22000000 + (0x300*32) + (2*4).

 

Writing to address 0x22006008 has the same effect as a read-modify-write operation on bit

 

2 of the byte at SRAM address 0x20000300.

 

Reading address 0x22006008 returns the value (0x01 or 0x00) of bit 2 of the byte at SRAM

 

address 0x20000300 (0x01: bit set; 0x00: bit reset).

 

For more information on Bit-Banding, please refer to the Cortex®-M3 Technical Reference

 

Manual.

[mh.ferris9]

Posted on August 18, 2015 at 13:28

Still not quite sure what you're worried about?

Are you writing code in assembler or C?

[antonius]

Posted on August 18, 2015 at 14:20

I'm writing on C,

I want to know the address of the data for reading and writing later on...

How can I point to one address and write ? then read ?

for example

write at the location 0x020000 = ''a''....

then read from that location later on...

thanks

[Tesla DeLorean]

Posted on August 18, 2015 at 14:43

The linker assigns addresses to variables in SRAM. Review the .MAP output to see where they are, and what's being used.

int a = 123;

printf(''%p\n'', &a); // Print address of 'a'

*((uint32_t *)0x20002000) = 0x12345678;

printf(''%08X\n'', *((uint32_t *)0x20002000) );

[mh.ferris9]

Posted on August 18, 2015 at 14:57

Its trivial to write and read variables that are in RAM.

Do you want to write and read random addresses in RAM?  If so, what for?

[antonius]

Posted on August 18, 2015 at 15:17

Thanks clive,

I think I can see how it works from here :

STM32F10x_StdPeriph_Lib_V3.5.0/Project/STM32F10x_StdPeriph_Examples/Library_Examples.html

how do you reckon ?

Bit Banding

This example shows how to use CortexM3 Bit-Band access to perform atomic read-modify-write and read operations on a variable in SRAM.

[Tesla DeLorean]

Posted on August 18, 2015 at 16:29

Bit-Banding simply rebases the memory so that each bit is not represented by a 32-bit word.