Functional Description
ARM DDI 0275D
Copyright © 2002, 2003 ARM Limited. All rights reserved.
2-19
2.11
AHB transfers
This section describes:
•
•
2.11.1
Read transfer
Two types of read transfer are described:
•
•
Asynchronous HCLK and CLK
When
HSEL
goes HIGH, this indicates that an AHB transfer involving the ETB11
AHB interface has started. On the same cycle that
HSEL
is asserted, the type of transfer
and the address of the transfer are specified on
HWRITE
and
HADDR
respectively.
HReq
goes HIGH after
HSEL
goes HIGH, indicating the start of the synchronization
period between the
HCLK
and
CLK
domain if the
SBYPASS
signal is LOW.
HReq
is
registered twice in the
CLK
domain to form
CReq
. When
CReq
goes HIGH, the
address value on
HADDRReg
, the registered version of
HADDR
that remains valid
until
HReq
goes LOW, is valid. The
CS
and
CRegRead
signals that control read access
of the ETB11 RAM and the ETB11 registers go HIGH for one cycle after
CReq
goes
HIGH.
Data is returned from the ETB11 RAM or the ETB11 registers and registered into
CData
.
CAck
goes HIGH to indicate that the read value has been retrieved.
CAck
is registered twice in the
HCLK
domain to form
HAck
. After
HAck
goes HIGH,
HRDATAMEM
gets the value of
MuxedData
(a multiplexed version of the data
returned from RAM, registers, and
CData
) and
HREADYMEM
goes HIGH indicating
to the AHB bus master that the data on
HRDATAMEM
is valid.
HReq
then goes LOW, indicating that the AHB transfer has finished. This causes
CAck
to go LOW one cycle after
CReq
goes LOW.
Finally,
HAck
goes LOW, finishing the read cycle.
How the
CReq
,
CAck
, and
HAck
signals are produced is shown in Figure 2-8 on
Summary of Contents for ETB11
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Page 70: ...Signal Descriptions A 6 Copyright 2002 2003 ARM Limited All rights reserved ARM DDI 0275D ...
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