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diff --git a/notes/dma.txt b/notes/dma.txt new file mode 100644 index 0000000..97b23a0 --- /dev/null +++ b/notes/dma.txt @@ -0,0 +1,99 @@ +DMA Notes +========= + +Medium-density devices have one DMA controller, DMA1. High-density +devices and up also have DMA2. DMA1 has 7 channels; DMA2 has 5. Each +channel multiplexes DMA requests from various peripherals, like so: + +Channel Capabilities +-------------------- + +DMA1: + + * Channel 1: ADC1, TIM2_CH3, TIM4_CH1 + * Channel 2: USART3_TX, TIM1_CH1, TIM2_UP, TIM3_CH3, SPI1_RX + * Channel 3: USART3_RX, TIM1_CH2, TIM3_CH4, TIM3_UP, SPI1_TX + * Channel 4: USART1_TX, TIM1_CH4, TIM1_TRIG, TIM1_COM, TIM4_CH2, + SPI2/I2S2_RX, I2C2_TX + * Channel 5: USART1_RX, TIM1_UP, TIM2_CH1, TIM4_CH3, + SPI2/I2S2_TX, I2C2_RX + * Channel 6: USART2_RX, TIM1_CH3, TIM3_CH1, TIM3_TRIG, I2C1_TX + * Channel 7: USART2_TX, TIM2_CH2, TIM2_CH4, TIM4_UP, I2C1_RX + +DMA2: + + * Channel 1: TIM5_CH4, TIM5_TRIG, TIM8_CH3, TIM8_UP, SPI/I2S3_RX + * Channel 2: TIM8_CH4, TIM8_TRIG, TIM8_COM, TIM5_CH3, TIM5_UP, SPI/I2S3_TX + * Channel 3: TIM8_CH1, UART4_RX, TIM6_UP/DAC_CH1 + * Channel 4: TIM5_CH2, SDIO, TIM7_UP/DAC_CH2 + * Channel 5: ADC3, TIM8_CH2, TIM5_CH1, UART4_TX + +An example usage: via DMA1, channel 1, you can have ADC1 periodically +dump converted data into an array in memory. The DMA controller can +then interrupt you when the array is half-full and full, and if any +error occurred. + +Since channels are multiplexed in hardware, you can't simultaneously +use the same DMA channel to serve requests from two of its peripherals +at the same time. For example, if you are using DMA 1 channel 1 to +serve DMA requests from ADC1, you can't also serve requests from Timer +2 channel 3. + +Channel Priority +---------------- + +An arbiter prioritizes simultaneous channel DMA requests. Channel +priority levels are configurable (4 levels of priority). Ties within +a DMA controller are broken by choosing the lower channel number; +between the controllers, DMA1 has higher priority than DMA2. + +Interrupts +---------- + +You can cause an interrupt to fire once half the transfers are +complete, when all the transfers are complete, if an error occurs +during transfer, or any combination of the three. + +If an error occurs, the transfer is automatically disabled. + +Configuration +------------- + +In order to configure a DMA transfer for DMA controller n, channel x, +ST RM0008 says you should do the following: + + A. Set the peripheral register address in DMAn_BASE->CPARx. + B. Set the memory address in DMAn_BASE->CMARx. + C. Set the number of data to be transferred in DMAn_BASE->CNDTRx. + D. Set the channel priority via the PL bits in DMAn_BASE->CCRx. + E. Configure various other things (e.g. data transfer sizes, what + events cause channel interrupts) in DMAn_BASE->CCRx as desired. + F. Activate the channel by setting ENABLE bit in DMAn_BASE->CCRx. + +The channel will start serving DMA requests as soon as it's activated. + +The DMA library lets you accomplish these tasks as follows: + + **Setup transfer** + + Do (A), (B), and (E) using dma_setup_transfer(). + + This also does (D), but chooses the lowest priority by default. + + **Perform any other desired configuration** + + You can do (C) using dma_set_num_transfers(). + + You can do (D) using dma_set_priority(). + + You can attach interrupt handlers with dma_attach_interrupt(). + + **Activate the channel** + + Do (F) with dma_enable(). + +Once you're all done, you can dma_disable() the channel. If you +dma_detach_interrupt() an interrupt handler, the channel interrupts +will stop firing, but the transfer itself won't stop until it's done +(which never happens if you set the DMA_CIRC_MODE flag when you called +dma_setup_transfer()). |