External Core Complex Interfaces
e200z3 Power Architecture Core Reference Manual, Rev. 2
7-32
Freescale Semiconductor
7.5.1.1
Basic Read Transfer Cycles
During a read transfer, the core receives data from a memory or peripheral device.
shows
functional timing for basic read transfers, and clock-by-clock descriptions of activity follow.
Figure 7-3. Basic Read Transfer—Single-Cycle Reads, Full Pipelining
•
Clock 1 (C1)—The first read transfer starts in clock cycle 1. During C1, the core places valid values
on the address bus and transfer attributes. The burst type (p_[d,i]_hburst[2:0]), protection control
(p_[d,i]_hprot[5:0]), and transfer type (p_[d,i]_htrans[1:0]) attributes identify the specific access
type. The transfer size attributes (p_[d,i]_hsize[1:0]) indicate the size of the transfer. The byte
strobes (p_[d,i]_hbstrb[7:0]) are driven to indicate active byte lanes. The write (p_[d,i]_hwrite)
signal is driven low for a read cycle.
The core asserts a transfer request (p_[d,i]_htrans= NONSEQ) during C1 to indicate that a transfer
is being requested. Because the bus is currently idle, (0 transfers outstanding), the first read request
to addr
x
is considered taken at the end of C1. The default slave drives a ready/OKAY response for
the current idle cycle.
•
Clock 2 (C2)—During C2, the addr
x
memory access takes place, using the address and attribute
values that were driven during C1 to enable reading of 1 or more bytes of memory. Read data from
the slave device is provided on the p_[d,i]_hrdata inputs. The slave device responds by asserting
p_[d,i]_hready to indicate that the cycle is completing, and it drives an OKAY response.
Another read transfer request is made during C2 to addr
y
(p_[d,i]_htrans = NONSEQ), and
because the access to addr
x
is completing, it is considered taken at the end of C2.
•
Clock 3 (C3)—During C3, the addr
y
memory access takes place, using the address and attribute
values that were driven during C2 to enable reading of one or more bytes of memory. Read data
nonseq
nonseq
nonseq
idle
addr x
addr y
addr z
single
single
single
data x
data y
data z
okay
okay
okay
okay
1
2
3
4
5
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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