SDMA Channels and IDMA Emulation
MPC885 PowerQUICC Family Reference Manual, Rev. 2
19-16
Freescale Semiconductor
storage at the end of the bus cycle. For memory reads, SAPR is automatically incremented by 1, 2,
4, or 16, depending on the address and size information specified by DCMR. See
Section 19.3.2,
“IDMA Parameter RAM,”
and
Section 19.3.3.1, “DMA Channel Mode Registers (DCMR).”
•
Dual-address destination write—The data in internal storage is written to the peripheral or memory
governed by the address in DAPR, the address type in DFCR, and the size in DCMR. For memory
writes, DAPR is automatically incremented by 1, 2, 4, or 16 according to DCMR. The byte count
is decremented by the number of bytes transferred. When the byte count reaches zero and the
transfer reports no errors, IDSR[DONE] is flagged, which triggers a maskable interrupt. See
Section 19.3.2, “IDMA Parameter RAM,”
and
Section 19.3.3, “IDMA Registers.”
Additionally, for peripheral/memory dual-address transfers, the SDACK signal asserts during the
peripheral access. For dual-address transfers, microcode performs byte-packing using a 16-byte buffer in
the dual-port RAM. Regardless of the source size, destination size, source starting address, or destination
starting address, IDMA uses the most efficient packing algorithm possible to perform the transfer in the
least number of bus cycles.
19.3.8.2
Single-Address (Single-Cycle) Transfer (Fly-By)
Each IDMA channel can be independently programmed to provide single-address, or fly-by, transfers. The
IDMA channel bypasses or flies-by internal storage since the transfer occurs directly between a device and
memory. DCMR[S/D] controls the direction of the transfer. If DCMR[S/D] = 0b01, the IDMA controller
handshakes with the peripheral for the source data and writes to the destination memory address provided.
If DCMR[S/D] = 0b10, the IDMA controller handshakes with the destination peripheral and reads from
the source memory address provided. The single-address read and write cycles are described below.
•
Single-address memory-read/peripheral-write—The memory address in SAPR, the address type in
SFCR, and the size in DCMR provide the data and control signals to the data bus. This bus cycle
operates like a normal read bus cycle. The SAPR is incremented by 1, 2, or 4, according to the
programming of DCMR[SIZE]. The destination device is controlled by the IDMA handshake
signals DREQ and SDACK. Asserting SDACK provides write control to the destination device.
Figure 19-10
and
Figure 19-11
show the transaction timing diagrams for asynchronous and
synchronous single-address peripheral writes. See
Section 19.3.7, “IDMA Interface
Signals—DREQ and SDACK,”
for more on IDMA handshake signals.
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