Memory layout on a microcontroller (Flash, SRAM, EEPROM) in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable stored in Flash memory.

Embedded C

const char message[] [1] = "Hello";

Drag options to blanks, or click blank then click option'

APROGMEM

Bvolatile

Cstatic

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'volatile' instead of 'PROGMEM' for Flash storage.

The PROGMEM keyword tells the compiler to store the variable in Flash memory.

2fill in blank

medium

Complete the code to declare a variable stored in SRAM.

Embedded C

[1] int counter = 0;

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Aregister

Bvolatile

Cconst

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'register' which stores variable in CPU register, not SRAM.

The static keyword declares a variable stored in SRAM with persistent value inside the function or file.

3fill in blank

hard

Fix the error in the code to correctly declare a variable in EEPROM.

Embedded C

uint8_t [1] eeprom_var;

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APROGMEM

BEEMEM

Cvolatile

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'PROGMEM' which stores data in Flash, not EEPROM.

The EEMEM keyword is used to place variables in EEPROM memory.

4fill in blank

hard

Fill both blanks to create a dictionary of variable types and their memory sections.

Embedded C

const char* memory_map[] = {"Flash", [1], "SRAM", [2];

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A"PROGMEM"

B"volatile"

C"static"

D"EEMEM"

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing EEPROM keyword with SRAM.

Flash memory uses PROGMEM and SRAM variables often use static for persistence.

5fill in blank

hard

Fill all three blanks to complete the code that reads a byte from EEPROM and stores it in SRAM.

Embedded C

uint8_t [2] EEMEM;
uint8_t [1] = eeprom_read_byte((uint8_t*)[3]);

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Adata_sram

Bdata_eeprom

C&data_eeprom

Ddata_flash

Attempts:

3 left

💡 Hint

Common Mistakes

Passing variable instead of address to eeprom_read_byte.

data_sram stores the byte in SRAM, data_eeprom is the EEPROM variable, and &data_eeprom is the address passed to eeprom_read_byte.

Practice

1. Which type of memory in a microcontroller is used to store the program code permanently?

easy

A. SRAM

B. Flash memory

C. EEPROM

D. Cache memory

Solution

1. Step 1: Understand memory types

   Flash memory is non-volatile and stores the program code permanently.

2. Step 2: Compare with other memories

   SRAM is temporary for variables, EEPROM stores small data but not the main program.

3. Final Answer:

   Flash memory -> Option B

4. Quick Check:

   Program code = Flash memory [OK]

Hint: Program code is always in Flash memory [OK]

Common Mistakes:

• Confusing SRAM with Flash memory
• Thinking EEPROM stores program code
• Assuming cache memory is used in microcontrollers

2. Which of the following declarations correctly places a variable in EEPROM memory in embedded C?

easy

A. int var __attribute__((section(".eeprom")));

B. int var __attribute__((section(".sram")));

C. int var __attribute__((section(".flash")));

D. int var __attribute__((section(".stack")));

Solution

1. Step 1: Identify EEPROM section syntax

   Variables placed in EEPROM use the section attribute ".eeprom" in embedded C.

2. Step 2: Check other options

   ".sram" is for SRAM, ".flash" for Flash, ".stack" is not a valid section for variables.

3. Final Answer:

   int var __attribute__((section(".eeprom"))); -> Option A

4. Quick Check:

   EEPROM section attribute = .eeprom [OK]

Hint: EEPROM variables use section ".eeprom" attribute [OK]

Common Mistakes:

• Using .sram or .flash instead of .eeprom
• Forgetting __attribute__ syntax
• Confusing stack with memory sections

3. Consider this embedded C code snippet:

const int x = 10;
int y = 20;
int main() {
  static int z = 30;
  return 0;
}

Where are the variables x, y, and z stored respectively?

medium

A. x in SRAM, y in EEPROM, z in Flash

B. x in EEPROM, y in Flash, z in EEPROM

C. x in Flash, y in EEPROM, z in SRAM

D. x in Flash, y in SRAM, z in SRAM

Solution

1. Step 1: Analyze variable storage rules

   Constants like x are stored in Flash memory. Global variables like y go to SRAM. Static variables like z also reside in SRAM during runtime.

2. Step 2: Match variables to memory types

   x = Flash, y = SRAM, z = SRAM.

3. Final Answer:

   x in Flash, y in SRAM, z in SRAM -> Option D

4. Quick Check:

   const = Flash, global/static = SRAM [OK]

Hint: const vars in Flash, globals and statics in SRAM [OK]

Common Mistakes:

• Assuming static variables go to EEPROM
• Thinking const variables are in SRAM
• Mixing EEPROM with Flash for constants

4. This embedded C code tries to store a variable in EEPROM:

int var __attribute__((section(".eeprom"))) = 5;
void main() {
  var = 10;
}

What is the main problem with this code?

medium

A. You cannot assign a new value to EEPROM variable at runtime like this

B. The section attribute syntax is incorrect

C. Variables in EEPROM must be declared as const

D. The main function must return int, not void

Solution

1. Step 1: Understand EEPROM write limitations

   EEPROM variables cannot be assigned new values by simple assignment at runtime; special functions are needed to write EEPROM.

2. Step 2: Check other code aspects

   The section attribute syntax is correct, variables need not be const, and main can be void in embedded C.

3. Final Answer:

   You cannot assign a new value to EEPROM variable at runtime like this -> Option A

4. Quick Check:

   EEPROM write needs special functions [OK]

Hint: EEPROM writes need special functions, not simple assignment [OK]

Common Mistakes:

• Assuming normal assignment writes EEPROM
• Thinking section attribute is wrong
• Confusing main return type with memory issues

5. You want to store a configuration value that must persist after power off and be modifiable during runtime on a microcontroller. Which memory type should you use and why?

hard

A. Cache memory, because it stores frequently used data

B. Flash, because it is fast and can be rewritten easily during runtime

C. EEPROM, because it retains data without power and allows runtime updates with special functions

D. SRAM, because it is volatile and fast for temporary storage

Solution

1. Step 1: Identify memory needs

   The value must persist after power off and be modifiable during runtime.

2. Step 2: Match memory type to needs

   EEPROM is non-volatile and supports runtime updates via special functions. Flash is non-volatile but rewriting is slower and more complex. SRAM is volatile and loses data on power off. Cache is not used for persistent storage.

3. Final Answer:

   EEPROM, because it retains data without power and allows runtime updates with special functions -> Option C

4. Quick Check:

   Persistent modifiable data = EEPROM [OK]

Hint: Use EEPROM for persistent, modifiable data [OK]

Common Mistakes:

• Choosing Flash for frequent runtime updates
• Using SRAM for persistent storage
• Confusing cache with persistent memory