HD6417641 RENESAS [Renesas Technology Corp], HD6417641 Datasheet - Page 451

• Manufacturer Part Number: HD6417641
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 12 Bus State Controller (BSC)
12.5.13 Others
Reset: The bus state controller (BSC) can be initialized completely only at power-on reset. When
a power-on reset occurs, internal clocks are synchronized by the reset, then all signals are negated
and output buffers are turned off regardless of the bus cycle state. All control registers are
initialized.
In standby, sleep, and manual reset, control registers of the bus state controller are not initialized.
At manual reset, the current bus cycle being executed is completed and then the access wait state
is entered. If a 16-byte transfer is performed by a cache or if another LSI on-chip bus master
module is executed when a manual reset occurs, the current access is cancelled in longword units
because the access request is cancelled by the bus master at manual reset. If a manual reset is
requested during cache fill operations, the contents of the cache cannot be guaranteed. Since the
RTCNT continues counting up during manual reset signal assertion, a refresh request occurs to
initiate the refresh cycle. However, a bus arbitration request by the BREQ signal cannot be
accepted during manual reset signal assertion.
Some flash memories may specify a minimum time from reset release to the first access. To
ensure this minimum time, the bus state controller supports a 7-bit counter (RWTCNT). At power-
on reset, the RWTCNT is cleared to 0. After power-on reset, RWTCNT is counted up
synchronously together with CKIO and an external access will not be generated until RWTCNT is
counted up to H'007F. At manual reset, RWTCNT is not cleared.
Access from the Site of the LSI Internal Bus Master: There are three types of LSI internal
buses: a cache bus, internal bus, and peripheral bus. The CPU and cache memory are connected to
the cache bus. Internal bus masters other than the CPU and bus state controller are connected to
the internal bus. Low-speed peripheral modules are connected to the peripheral bus. Internal
memories other than the cache memory are connected bidirectionally to the cache bus and internal
bus. Access from the cache bus to the internal bus is enabled but access from the internal bus to
the cache bus is disabled. This gives rise to the following problems.
On-chip bus masters such as DMAC other than the CPU can access internal memory other than
the cache memory but cannot access the cache memory. If an on-chip bus master other than the
CPU writes data to an external memory other than the cache, the contents of the external memory
may differ from that of the cache memory. To prevent this problem, if the external memory whose
contents is cached is written by an on-chip bus master other than the CPU, the corresponding
cache memory should be purged by software.
Rev. 4.00 Sep. 14, 2005 Page 401 of 982
REJ09B0023-0400