DMA with UART for bulk transfer in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

DMA UART Bulk Transfer Initialization Output

What will be the output of this embedded C code snippet that initializes DMA for UART bulk transfer and starts the transfer?

Embedded C

#include <stdio.h>
#include <string.h>

// Simulated UART and DMA registers
volatile int UART_TX_READY = 1;
volatile int DMA_TRANSFER_COMPLETE = 0;

void DMA_StartTransfer(char *buffer, int length) {
    if (UART_TX_READY) {
        printf("DMA started for %d bytes\n", length);
        DMA_TRANSFER_COMPLETE = 1;
    } else {
        printf("UART not ready\n");
    }
}

int main() {
    char data[] = "Hello DMA UART!";
    DMA_StartTransfer(data, strlen(data));
    if (DMA_TRANSFER_COMPLETE) {
        printf("DMA transfer complete\n");
    } else {
        printf("DMA transfer not complete\n");
    }
    return 0;
}

A

DMA started for 15 bytes
DMA transfer complete

B

UART not ready
DMA transfer not complete

C

DMA started for 14 bytes
DMA transfer complete

D

DMA started for 15 bytes
DMA transfer not complete

💡 Hint

Check the length of the string passed to DMA_StartTransfer and the UART_TX_READY flag.

The string "Hello DMA UART!" has 15 characters including spaces and punctuation. UART_TX_READY is 1, so DMA starts and sets DMA_TRANSFER_COMPLETE to 1. The output matches option A.

🧠 Conceptual

intermediate

DMA and UART Bulk Transfer Buffer Size

In a DMA-based UART bulk transfer, why is it important to correctly configure the DMA buffer size?

A Because the DMA buffer size controls the UART baud rate directly.

B Because the DMA buffer size determines how many bytes are transferred in one operation, preventing data overflow or truncation.

C Because the DMA buffer size sets the UART parity bits automatically.

D Because the DMA buffer size decides the CPU clock speed during transfer.

💡 Hint

Think about how DMA moves data and what happens if the buffer is too small or too large.

The DMA buffer size defines how many bytes the DMA controller transfers in one go. If it's too small, data may be lost or require multiple transfers. If too large, it may cause memory issues. It does not affect UART baud rate, parity, or CPU clock.

🔧 Debug

advanced

Identify the Bug in DMA UART Transfer Code

What error will this code cause when running a DMA UART bulk transfer?

Embedded C

char uart_buffer[10];
void start_dma_transfer() {
    // Intentionally incorrect length
    int length = 20;
    DMA_StartTransfer(uart_buffer, length);
}

void DMA_StartTransfer(char *buffer, int length) {
    // Simulated transfer
    printf("Transferring %d bytes\n", length);
}

A Buffer overflow because length exceeds buffer size

B Syntax error due to missing semicolon

C No output because DMA_StartTransfer is never called

D Runtime error due to null pointer

💡 Hint

Check the buffer size and the length passed to DMA_StartTransfer.

The buffer uart_buffer is only 10 bytes, but the code tries to transfer 20 bytes, causing a buffer overflow risk. This can lead to memory corruption or crashes.

📝 Syntax

advanced

Syntax Error in DMA UART Transfer Setup

Which option contains the correct syntax to configure DMA for UART transmission in embedded C?

Embedded C

/* Assume DMA_Config is a struct with fields: source, destination, length */
DMA_Config dma_cfg;
dma_cfg.source = uart_tx_buffer;
dma_cfg.destination = UART_DATA_REGISTER;
dma_cfg.length = 64;

A

dma_cfg.source = uart_tx_buffer;
 dma_cfg.destination = UART_DATA_REGISTER
 dma_cfg.length = 64;

B

dma_cfg.source = uart_tx_buffer
 dma_cfg.destination = UART_DATA_REGISTER;
 dma_cfg.length = 64;

C

dma_cfg.source := uart_tx_buffer;
 dma_cfg.destination := UART_DATA_REGISTER;
 dma_cfg.length := 64;

D

dma_cfg.source = uart_tx_buffer;
 dma_cfg.destination = UART_DATA_REGISTER;
 dma_cfg.length = 64;

💡 Hint

Remember the correct statement terminator in C.

In C, each statement must end with a semicolon. Option D correctly uses semicolons on all lines. Option D and D miss semicolons on some lines. Option D uses := which is invalid in C.

🚀 Application

expert

Calculate Total Bytes Transferred in DMA UART Bulk Transfer

Given a DMA UART bulk transfer configured with a buffer size of 128 bytes and a transfer count of 10, what is the total number of bytes transferred?

A 10 bytes

B 138 bytes

C 1280 bytes

D 128 bytes

💡 Hint

Multiply buffer size by transfer count to get total bytes.

Total bytes transferred equals buffer size multiplied by the number of transfers: 128 * 10 = 1280 bytes.