DMA Modules
• The STM32 has two DMA peripherals each of which
has multiple inde- pendently configurable “channels”
(7 for DMA1 and 5 for DMA2). A channel is roughly the
hardware realization of a transaction.
• To initialize DMA be- tween a peripheral and memory it
is necessary to configure the appropriate channel. For
example, DMA1 channel 2 (3) can be used to receive
(transmit) data from (to) SPI1.
DMA Settings
• Prior to utilizing the DMA peripherals,
remember to enable their clocks
• Configuring a channel consists of setting
appropriate parameters through a
DMA_InitTypeDef structure
The parameters include the peripheral base address (e.g. ADC1>DR), the memory address buffer, the transfer direction, the buffer
size, etc. Once the DMA channel is initialized, it must be enabled.
The STM32 firmware provides peripheral specific commands to
enable a DMA transaction.
• DMA module must be activated in the module
which uses DMA:
ADC_DMACmd(ADC1, ENABLE);
ADC_DMARequestAfterLastTransferCmd(ADC1,ENABLE);
Or
The DMA channels provided by the STM32 are each associated
with specific peripherals (See reference manual for complete
documentation). For example DMA1 channel 1 supports ADC1,
TIM2_CH3, and TIM4_CH1.
DAC Module
• The DAC module is a 12-bit, voltage output digital-toanalog converter.
• The DAC can be configured in 8- or 12-bit mode and
may be used in conjunction with the DMA controller.
• The DAC has two output channels, each with its own
converter– DAC1 (pin PA4) and DAC2 (pin PA5)
• In dual DAC channel mode, conversions could be done
independently or simultaneously when both channels
are grouped together for synchronous update
operations. An
• input reference pin, Vref+(shared with ADC) is available
for better resolution.
Each channel has separate
control logic which is configured
through a single control register
(CR). Data to be converted by
channel x are written to data
holding register (DHRx). In
response to a trigger event,
DHRx is transferred to the data
output register (DORx) and, after
a settling time, the
corresponding analog value
appears at the output.
DAC Settings
• The clock sources must be activated and the DAC (PA4 or
PA5) pin must be configured as “analog ”.
•
• Once a DAC is initialized, data may be written
using the following commands
DAC Functions (CMSIS)
Pulse Width Modulation
•
•
•
•
PWM signal
Duty Cycle, freq.
Sinosoidal signal
Applications:
– Servo driver
– SMPS
– etc.
Timer PWM Settings
The pulse- width pw (0..999) can be set
with the following command.
The pulse- width pw (0..999) can be set with the following command.
Test_dma_adc
• Configure ADC1 and ADC2 in simultaneous mode, Set
the DMA2 to transfer the ADC results to a mem. region
• Configure TIM2-> update at 50 KHz
• Configure the TIM2 output trigger so that it occurs on
update events:
TIM_SelectOutputTrigger(TIM2,TIM_TRGOSource_Update);
• Change the trigger in the ADC initialization code:
ADC_InitStructure.ADC_ExternalTrigConv=ADC_ExternalTrigConv_T2_TRGO;
• Configure the NVIC to enable interrupt channel
DMA_IRQn with the highest priority
• Write a suitable interrupt handler.
Test_dac
• Enable DAC_Channel_1
• Set TIM2 interrupt  150 KHz
• Configure the NVIC to enable interrupt
channel TIM2_IRQn with the highest priority
• Write a suitable interrupt handler.
Test_dac_speech
• Homework