TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-43
V2.0, 2007-07
EBU, V2.0
13.7.2
Command Delay Phase (CD)
The Command Delay phase is optional. This means that it can also be programmed for
a length of zero LMBCLK clock cycles. The CD phase allows for the insertion of a delay
between Address Phase and Command Phase(s). This phase accommodates devices
that are not fast enough to receive commands immediately after getting the address.
The length (number of LMBCLK cycles) of the Command Delay phase is programmed
via the EBU_BUSAPx.CMDDELAY bit field. This parameter makes it possible to select
between zero to seven Command Delay phases. Additionally, the number of Command
Delay phases as selected via ADDRC can be multiplied by the EBU_BUSCONx.CMULT
parameter, but only if bit EBU_BUSCONx.MULTMAP[2] is set (CMDDELAY multiplier
function enabled).
The calculation of the number of LMBCLK cycles in the Command Delay phase is
defined in the following table:
The equivalent control capability is available for bit field EBU_EMUBAP.CMDDELAY,
which can be multiplied by EBU_EMUBC.CMULT if bit EBU_EMUBC.MULTMAP[2] is
set.
13.7.3
Command Phase (CP)
The Command Phase is mandatory. It always consists of at least one or more LMBCLK
cycles. The phase can optionally be extended to accommodate slower devices.
The length (number of LMBCLK cycles) of the Command Phase is separately
programmable for read and write accesses. Bit field EBU_BUSAPx.WAITRDC
determines the basic length of Command Phases during read cycles and bit field
EBU_BUSAPx.WAITWRC determines the basic length of Command Phases during
write cycles. One to seven LMBCLK cycles can be programmed for these two
parameters. The total number of LMBCLK cycles in Command Phases during read and
write accesses is calculated by multiplying WAITRDC and WAITWRC by the parameter
as selected by bit field EBU_BUSCONx.CMULT (independently of bit field
EBU_BUSCONx.MULTMAP).
The calculation of the number of Command Phase LMBCLK cycles is described in the
following table:
MULTMAP
Number of Command Delay Phase Cycles
XXXX0XX
B
= CMDDELAY
XXXX1XX
B
= CMDDELAY
×
CMULT