External Core Complex Interfaces
e200z3 Power Architecture Core Reference Manual, Rev. 2
Freescale Semiconductor
7-55
Figure 7-26. Burst Read with Error Termination, Burst Write
The first portion of the burst read request is terminated with error. The second portion is aborted by the
CPU during the second cycle of the two cycle error response, and a subsequent burst write access to addr
y
becomes pending instead.
7.5.4
Address Retraction
Address retraction is the process of replacing a request with a new unrelated one. Although the AMBA
AHB protocol requires an access request to remain driven unchanged once presented on the bus, higher
system performance may be obtained if this aspect of the protocol is modified to allow an access request
to be changed before being taken.
shows an example of address retraction during wait state
operation. Signal p_hready for the first request (addr
x
) is not asserted during C2, so a wait state is inserted
during C3 until p_hready is recognized.
Meanwhile, a subsequent request has been generated by the CPU for addr
y
which is not taken in C2 since
the previous transaction is still outstanding. The address and transfer attributes are retracted in cycle C3,
and a new access to addr
z
is requested and made at the end of C3 because the previous access is
completing. Data for addr
x
and a ready/OKAY response are driven back by the slave device. In cycle C4,
a request for addr
w
is made. The request for access to addr
w
is taken at the end of C4; during C5, the data
and a ready/OKAY response are provided by the slave device. In cycle C5, no further accesses are
requested.
nonseq
seq
idle
nonseq
seq
seq
seq
idle
addr x
addr x+8
addr y
addr y+8
addr y+16
addr y+24
wrap4
wrap4
data x
data y
y+8
y+16
y+24
okay
error
error
okay
okay
okay
okay
okay
1
2
3
4
5
6
7
8
m_clk
p_htrans
p_addr,p_hprot
p_hsize
,
p_hbstrb
, etc
p_hburst
p_hunalign
p_hwrite
p_hrdata
p_hwdata
p_hready
p_hresp
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