Freescale Semiconductor MPC8260 19.5 IDMA Transfers

SDMA Channels and IDMA Emulation
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
19-6 Freescale Semiconductor
• Programmable byte-order conversion is supported independently for each DMA channel
• Supports programmable 60x-bus bandwidth usage for system performance optimization
Peripheral to/from memory features include the following:
• External DREQ, DACK, and DONE signals for each channel simplifies the peripheral interf ace for
memory-to/from-peripheral transfers
• Supports 1-, 2-, 4-, and 8-byte peripheral port sizes
• Supports standard 60x burst accesses (four consecutive 64-bit data phases) to/from peripherals
19.5 IDMA Transfers
The IDMA channel transfers data from a source to a destination using an intermediate transfer buffer (of
programmable size) in the dual-port RAM (note that the IDMA cannot burst to or from the dual-port
RAM). An efficient data-packing algorithm bursts data through the IDMA transfer buffer to minimize the
bus cycles needed for the transfer; however, the IDMA will burst when it has 0x10 or more bytes to
transfer. In single-address peripheral transfers, however, data is transferred directly between memory and
a peripheral device without using the IDMA transfer buffer.
Unaligned data is transferred in single accesses until alignment is achieved. Then, burst transactions are
used (if allowed by the user) to transfer the bulk of the data buffer. Single accesses are used again for any
remaining non-burstable data at the end of the transfer.
19.5.1 Memory-to-Memory Transfers
For memory-to-memory transfers, the IDMA first fills the IDMA transfer buffer in the dual-port RAM by
initiating read accesses on the source bus. It then empties the data from the internal transfer buffer to the
destination bus by initiating write accesses. The transfer sizes for the source and destination buses are
programmed in the IDMA parameter RAM.
For the DMA to generate bursts on the 60x bus, the address boundaries of each burst trans fer must be
32-byte aligned. If the transfer does not start on a burst boundary, the IDMA controller transfers the
end-of-burst (EOB) data (1–31 bytes) in non-burst transactions on the source bus and on the destination
bus until reaching the next boundary. When alignment is achieved, subsequent data is bursted until the
remainder of the data in the buffer is less than a burst size (32 bytes). The remaining data is transferred
using non-burst transactions.
Data transfers use the parameters described in Table19-3.
Table19-3. IDMA Transfer Parameters
Parameter Description
DMA_WRAP Determines the size of the dedicated IDMA transfer buffer in dual-port RAM. The buffer size is a
multiple of a 60x burst size (k*32 bytes).