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2012-04-24 - Giant Gecko Family - d0053_Rev0.96 71
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individual DMA channels remember source and destination end pointers while active, speeding up their
transfers.
8.4.6 Interaction with the EMU
The DMA interacts with the Energy Management Unit (EMU) to allow transfers from e.g. the LEUART
to occur in EM2. The EMU can wake up the DMA sufficiently long to allow data transfers to occur. See
section "DMA Support" in the LEUART documentation.
8.4.7 Interrupts
The PL230 dma_done[n:0] signals, one for each channel, as well as the dma_err signal, are available as
interrupts to the Cortex-M3 core. They are combined into one interrupt vector, DMA_INT. If interrupts for
the DMA is enabled in the ARM Cortex-M3 core, an interrupt will be made if one or more of the interrupt
flags in DMA_IF and their corresponding bits in DMA_IEN are set.
8.5 Examples
A basic example of how to program the DMA for transferring 42 bytes from the USART1 to
memory location 0x20003420. Assumes that the channel 0 is currently disabled, and that the
DMA_ALTCTRLBASE register has already been configured.
Example 8.1. DMA Transfer
1. Configure the channel select for using USART1 with DMA channel 0
a. Write SOURCESEL=0b001101 and SIGSEL=XX to DMA_CHCTRL0
2. Configure the primary channel descriptor for DMA channel 0
a. Write XX (read address of USART1) to src_data_end_ptr
b. Write 0x20003420 + 40 to dst_data_end_ptr c
c. Write these values to channel_cfg for channel 0:
i. dst_inc=b01 (destination halfword address increment)
ii. dst_size=b01 (halfword transfer size)
iii. src_inc=b11 (no address increment for source)
iv. src_size=01 (halfword transfer size)
v. dst_prot_ctrl=000 (no cache/buffer/privilege)
vi. src_prot_ctrl=000 (no cache/buffer/privilege)
vii.R_power=b0000 (arbitrate after each DMA transfer)
viii.n_minus_1=d20 (transfer 21 halfwords)
ix. next_useburst=b0 (not applicable)
x. cycle_ctrl=b001 (basic operating mode)
3. Enable the DMA
a. Write EN=1 to DMA_CONFIG
4. Disable the single requests for channel 0 (i.e. do not react to data available, wait for buffer full)
a. Write DMA_CHUSEBURSTS[0]=1
5. Enable buffer-full requests for channel 0
a. Write DMA_CHREQMASKC[0]=1
6. 6. Use the primary data structure for channel 0
a. Write DMA_CHALTC[0]=1
7. 7. Enable channel 0
a. Write DMA_CHENS[0]=1