GPMC
When a delay larger than two GPMC clock cycles must be observed between wait-pin deassertion time
and the effective data write into the external device (including the required GPMC data setup time and the
device data setup time), an extra delay can be added between wait-pin deassertion time detection and
effective data write time into the external device and the effective unfreezing of the CYCLETIME counter.
This extra delay can be programmed in the GPMC_CONFIG1_i[19-18] WAITMONITORINGTIME fields.
•
The WAITMONITORINGTIME parameter does not delay the wait-pin assertion or deassertion
detection, nor does it modify the two GPMC clock cycles pipelined detection delay.
•
This extra delay is expressed as a number of GPMC_CLK clock cycles, even though the access is
defined as asynchronous, and even though no clock is provided to the external device. Still,
GPMC_CONFIG1_i[1-0] GPMCFCLKDIVIDER is used as a divider for the GPMC clock and so it must
be programmed to define the correct WAITMONITORINGTIME delay.
7.1.3.3.8.3.4 Wait Monitoring During a Synchronous Read Access
During synchronous accesses with wait-pin monitoring enabled, the wait pin is captured synchronously
with GPMC_CLK, using the rising edge of this clock.
The WAIT signal can be programmed to apply to the same clock cycle it is captured in. Alternatively, it can
be sampled one or two GPMC_CLK cycles ahead of the clock cycle it applies to. This pipelining is
applicable to the entire burst access, and to all data phase in the burst access. This WAIT pipelining depth
is programmed in the GPMC_CONFIG1_i[19-18] WAITMONITORINGTIME field, and is expressed as a
number of GPMC_CLK clock cycles.
In synchronous mode, when wait-pin monitoring is enabled (GPMC_CONFIG1_i[22]
WAITREADMONITORING bit), the effective access time is a logical AND combination of the
RDACCESSTIME timing completion and the WAIT deasserted-state detection.
Depending on the programmed WAITMONITORINGTIME value, the wait pin should be at a valid level,
either asserted or deasserted:
•
In the same clock cycle the data is valid if WAITMONITORINGTIME = 0 ( at RDACCESSTIME
completion)
•
In the WAITMONITORINGTIME x (GPMCFCLKD 1) GPMC_FCLK clock cycles before
RDACCESSTIME completion if WAITMONITORINGTIME not equal to 0
Similarly, during a multiple-access cycle (burst mode), the effective access time is a logical AND
combination of PAGEBURSTACCESSTIME timing completion and the wait-inactive state. The Wait
pipelining depth programming applies to the whole burst access.
•
WAIT monitored as active freezes the CYCLETIME counter. For an access within a burst (when the
CYCLETIME counter is by definition in a lock state), WAIT monitored as active extends the current
access time in the burst. Control signals are kept in their current state. The data bus is considered
invalid, and no data are captured during this clock cycle.
•
WAIT monitored as inactive unfreezes the CYCLETIME counter. For an access within a burst (when
the CYCLETIME counter is by definition in lock state), WAIT monitored as inactive completes the
current access time and starts the next access phase in the burst. The data bus is considered valid,
and data are captured during this clock cycle. In a single access or if this was the last access in a
multiple-access cycle, all signals are controlled according to their relative control timing value and the
CYCLETIME counter status.
shows wait behavior during a synchronous read burst access.
268
Memory Subsystem
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated
