![Marvell PXA300 Скачать руководство пользователя страница 327](http://html.mh-extra.com/html/marvell/pxa300/pxa300_developers-manual_1734615327.webp)
69rlq62d-f714peg4 * Memec (Headquar
ter
s) - Unique
Tec
h,
Insight,
Impact
MAR
VELL CONFIDENTIAL,
UNDER ND
A# 12101050
69rlq62d-f714peg4 * Memec (Headquar
ter
s) - Unique
Tec
h,
Insight,
Impact
MAR
VELL CONFIDENTIAL,
UNDER ND
A# 12101050
69r
lq62d-f714peg4 * Memec (Headquar
ters) - Unique
T
ech, Insight, Impact * UNDER ND
A# 12101050
MAR
VELL CONFIDENTIAL - UNA
UTHORIZED DISTRIB
UTION OR USE STRICTL
Y PR
OHIBITED
DMA Controller
Copyright © 12/13/06 Marvell
CONFIDENTIAL
Doc. No. MV-TBD-00 Rev. A
December 13, 2006
Document Classification: Proprietary Information
Page 327
Not approved by Document Control. For review only.
11.4.6
DREQ Status Register (DRQSR0)
DRQSR0 (
) logs the number of pending requests made by an external companion chip on the
corresponding DREQ pin. The register reflects the status of a 5-bit counter that is controlled by the DMAC in the
following manner:
•
The DMAC increments the counter each time the external companion chip toggles the DREQ pin from low
to high (positive edge trigger). The external companion chip must follow the rules outlined in
•
For a write to an external peripheral, the DMAC decreases the counter after it completes the write.
•
For a read from an external peripheral, the DMAC decreases the counter after it sends the corresponding
read request to the memory controller.
12:0
R/W
LEN
Length of the transfer in bytes
This bit is the length of transfer in bytes. LEN = 0 means zero bytes for
descriptor-fetch transactions. LEN = 0 is an invalid setting for
no-descriptor-fetch transactions. Programming LEN = 0 in the
descriptor-fetch mode when DCMD[CmpEn] is clear (normal data transfer
mode) causes the channel to immediately discard the descriptor after it is
fetched from memory. If the descriptor chain has more descriptors, the
channel fetches the next valid descriptor. The channel stops if the
descriptor chain has no more descriptors. The maximum transfer length is
(8K-1) bytes.
If the transfer is of the memory-to-memory type, the length of the transfer
may be any value (except for the DCMDx[LEN] = 0 restriction in
no-descriptor-fetch mode) up to a maximum of (8K -1) bytes. If the transfer
involves an external peripheral (or a companion chip), then the length of the
transfer must be an integer multiple of the peripheral FIFO threshold (or
water-mark).
If the transfer involves any of the on-chip peripherals, the length of the
transfer must be as follows:
1. For AC ’97 and MMC/SDIO, LEN must be an integer multiple of 32
bytes.
2. For all other on-chip peripherals, LEN must be an integer multiple of the
peripheral’s sample width (DCMDx[WIDTH]).
NOTE:
LEN is ignored in the compare descriptor mode (when
DCMD[CMPEN] is set).
Table 11-13. DCMD0–31 Bit Definitions (Sheet 4 of 4)
Physical Address
0x4000_02xC–0x4000_03xC
DCMD0–DCMD31
DMA Controller
User
Settings
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
IN
CS
RCAD
DR
IN
CT
RGAD
DR
FLOWS
RC
FLOWT
RG
Reserved
CMP
E
N
Reserved
ADDRM
O
D
E
ST
A
R
T
IR
QE
N
E
N
DI
RQE
N
Reserved
SIZE
WI
D
T
H
Reserved
LEN
Reset
0
0
0
0
?
?
0
0
0
0
0
?
?
?
0
0
0
0
?
0
0
0
0
0
0
0
0
0
0
0
0
0
Bits
Access
Name
Description