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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
584 of 808
NXP Semiconductors
UM10360
Chapter 31: LPC17xx General Purpose DMA (GPDMA) controller
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If the DMACCxLLI Register is not 0, then reload the DMACCxSrcAddr,
DMACCxDestAddr, DMACCxLLI, and DMACCxControl Registers and go to back
to step 2. However, if DMACCxLLI is 0, the DMA stream is disabled and the flow
sequence ends.
Note:
Memory-to-memory transfers should be programmed with a low channel priority,
otherwise other DMA channels cannot access the bus until the memory-to-memory
transfer has finished, or other AHB masters cannot perform any transaction.
6.3 Interrupt requests
Interrupt requests can be generated when an AHB error is encountered or at the end of a
transfer (terminal count), after all the data corresponding to the current LLI has been
transferred to the destination. The interrupts can be masked by programming bits in the
relevant DMACCxControl and DMACCxConfig Channel Registers. The interrupt requests
from all DMA channels can be found in the DMACRawIntTCStat and DMACRawIntErrStat
registers. The masked versions of the DMA interrupt data is contained in the
DMACIntTCStat and DMACIntErrStat registers. The DMACIntStat register then combines
the DMACIntTCStat and DMACIntErrStat requests into a single register to enable the
source of an interrupt to be found quickly. Writing to the DMACIntTCClear or the
DMACIntErrClr Registers with a bit set to 1 enables selective clearing of interrupts.
6.3.1 Hardware interrupt sequence flow
When a DMA interrupt request occurs, the Interrupt Service Routine needs to:
1. Read the DMACIntTCStat Register to determine whether the interrupt was generated
due to the end of the transfer (terminal count). A 1 bit indicates that the transfer
completed. If more than one request is active, it is recommended that the highest
priority channels be checked first.
2. Read the DMACIntErrStat Register to determine whether the interrupt was generated
due to an error occurring. A 1 bit indicates that an error occurred.
3. Service the interrupt request.
4. For a terminal count interrupt, write a 1 to the relevant bit of the DMACIntTCClr
Register. For an error interrupt write a 1 to the relevant bit of the DMACIntErrClr
Register to clear the interrupt request.
6.4 Address generation
Address generation can be either incrementing or non-incrementing (address wrapping is
not supported).
Some devices, especially memories, disallow burst accesses across certain address
boundaries. The DMA controller assumes that this is the case with any source or
destination area, which is configured for incrementing addressing. This boundary is
assumed to be aligned with the specified burst size. For example, if the channel is set for
16-transfer burst to a 32-bit wide device then the boundary is 64-bytes aligned (that is
address bits [5:0] equal 0). If a DMA burst is to cross one of these boundaries, then,
instead of a burst, that transfer is split into separate AHB transactions.