TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-47
V2.0, 2007-07
EBU, V2.0
13.7.6
Recovery Phase (RP)
The Recovery Phase is optional. This means that it can also be programmed for a length
of zero LMBCLK clock cycles. This phase allows the insertion of a delay following an
external bus access that delays the start of the Address Phase for the next external bus
access. This permits flexible adjustment of the delay between accesses to the various
external devices. The following individually programmable delays are provided on a
region by region basis for the following conditions:
•
Bit fields EBU_BUSAPx.RDRECOVC and EBU_EMUBAPx.RDRECOVC determine
the basic length of the Recovery Phase after a read access.
•
Bit fields EBU_BUSAPx.WRRECOVC and EBU_EMUBAPx.WRRECOVC determine
the basic length of the Recovery Phase after a write access.
•
Bit fields EBU_BUSAPx.DTARDWR and EBU_EMUBAPx.DTARDWR determine the
length (basic number of LMBCLK clock cycles) of the Recovery Phase after a write
access that is followed by a read access, or after a read access that is followed by a
write access.
•
Bit fields EBU_BUSAPx.DTACS and EBU_EMUBAPx.DTACS determine the length
(basic number of LMBCLK clock cycles) of the Recovery Phase after a read/write
access of one region that is followed by a read/write access of another region.
The calculation of the total numbers of Recovery Phase clock cycles for each of the four
Recovery Phase parameters is described in the following table:
The EBU implements a “highest wins” algorithm to ensure that the longest applicable
recovery delay is always used between consecutive accesses to the external bus.
shows the scheme for determining this delay for all possible circumstances.
For example, if a read access to a region associated with CS1 is followed by a write to
a region associated with CS2, the delay will be the highest of DTARDWR, DTACS and
RDRECOVC. In this case, if DTARDWR is greater than DTACS and RDRECOVC, then
the number of recovery cycles between the two accesses is DTARDWR.
Parameter
MULTMAP
Number of Burst Phase Cycles
RDRECOVC
X0XXXXX
B
= RDRECOVC
X1XXXXX
B
= RDRECOVC
×
CMULT
WRRECOVC
0XXXXXX
B
= RDRECOVC
1XXXXXX
B
= RDRECOVC
×
CMULT
DTARDWR
–
= DTARDWR
×
CMULT
DTACS
–
= DTACS
×
CMULT