DMA with UART for bulk transfer in Embedded C - Step-by-Step Execution

Concept Flow - DMA with UART for bulk transfer

Start UART DMA Transfer

↓

Configure DMA with buffer

↓

Enable UART DMA Request

↓

DMA Transfers Data Automatically

↓

DMA Transfer Complete Interrupt

↓

Process Received Data

↓

End

The flow shows how DMA is set up to transfer data from UART automatically, triggering an interrupt when done.

Execution Sample

Embedded C

void start_uart_dma(void) {
  DMA_Config(UART_DR, buffer, size);
  UART_EnableDMA();
  DMA_Start();
}

void DMA_IRQHandler(void) {
  if (DMA_TransferComplete()) {
    process_data(buffer);
  }
}

This code configures DMA to transfer data from UART to a buffer and processes data when transfer completes.

Execution Table

Step	Action	DMA State	UART State	Buffer Content	Interrupt
1	Configure DMA with buffer and size	Configured	Idle	Empty	No
2	Enable UART DMA request	Configured	Ready for DMA	Empty	No
3	Start DMA transfer	Running	Receiving Data	Filling...	No
4	DMA transfers bytes automatically	Running	Receiving Data	Partial Data	No
5	DMA transfer completes full size	Complete	Idle	Full Data	Yes
6	DMA interrupt triggers	Complete	Idle	Full Data	Yes
7	Process received data in buffer	Idle	Idle	Processed Data	No
8	End of transfer cycle	Idle	Idle	Processed Data	No

💡 DMA transfer completes full size, triggers interrupt, then data is processed.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
DMA State	Not Configured	Running	Complete	Idle	Idle
UART State	Idle	Receiving Data	Idle	Idle	Idle
Buffer Content	Empty	Filling...	Full Data	Processed Data	Processed Data
Interrupt	No	No	Yes	No	No

Key Moments - 3 Insights

Why does the DMA transfer happen without CPU intervention?

Because DMA is configured to move data directly from UART to buffer automatically (see execution_table steps 3-5).

When does the CPU get notified that data transfer is complete?

CPU is notified by the DMA transfer complete interrupt at step 6 in the execution_table.

What happens to the buffer content after DMA transfer completes?

Buffer contains full data and then is processed by CPU as shown in steps 5 to 7.

Visual Quiz - 3 Questions

Look at the execution_table, what is the DMA State at step 4?

A Configured

B Complete

C Running

D Idle

💡 Hint

Check the DMA State column at step 4 in the execution_table.

At which step does the DMA interrupt trigger?

A Step 5

B Step 6

C Step 3

D Step 7

💡 Hint

Look for the Interrupt column showing 'Yes' in the execution_table.

If the buffer size was smaller, how would the Buffer Content at step 5 change?

A It would have partial data

B It would be empty

C It would have full data as before

D It would cause an error

💡 Hint

Refer to Buffer Content changes in variable_tracker and execution_table steps 4 and 5.

Concept Snapshot

DMA with UART bulk transfer:
- Configure DMA with buffer and size
- Enable UART DMA request
- Start DMA transfer (automatic data move)
- DMA triggers interrupt on completion
- CPU processes data from buffer
- Reduces CPU load during data reception

Full Transcript

This visual execution trace shows how DMA works with UART for bulk data transfer. First, DMA is configured with a buffer and size. Then UART DMA request is enabled. When DMA starts, it automatically transfers data from UART to the buffer without CPU intervention. Once the full data size is transferred, DMA triggers an interrupt to notify the CPU. The CPU then processes the received data in the buffer. This method reduces CPU load and allows efficient data reception.