TX4939 Datasheet, PDF (460/756 Pages) Toshiba Semiconductor – 64-Bit TX System RISC

PCIC
Toshiba RISC Processor
TX4939
16.6. A Malfunction of PCI Controller
16.6.1. Outline of the problem
If PCI to G-Bus transfer (PCI initiator read) by PDMAC, PCI read access by G-Bus bus master (B), and PCI bus access
(read or write) by G-Bus bus master (A) are executed simultaneously, PCI read access by G-Bus bus master (B) could not
finish.
16.6.2. Condition of the problem occurrence
(1) PDMAC PCI Initiator reads data from a device on PCI bus. (Read from PCI bus and write to G-Bus.)
(2) If an access (read or write) requirement (*) to a device on PCI bus by G-Bus bus master (A) is issued
before PDMAC PCI initiator’s read transfer (1) finish, the required access by G-Bus bus master (A) will
be retried on G-Bus.
By the way, the retry happened by overflow of PCI access command queue could cause the problem.
The followings are candidates to cause that retry.
The access requirement (*) by G-Bus bus master (A) is :
□ Burst Write Transfer
□ Single write transfer in case of that three times single write transfers are executed before
PDMAC PCI initiator read transfer (1)
□ (Single/Burst) read transfer in case of that three times single write transfers are executed
before PDMAC PCI initiator read transfer (1)
(3) PDMAC initiator read transfer (1) finish on PCI bus.
(4) Though read transfer on PCI bus by G-Bus bus master (B) is executed, it will be retried, and then the
retry can’t be accepted. Then retry → refuse the request → retry → refuse the request → … This
iteration will be continued permanently.
16.6.3. Work-around
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In case of that PCI to G-Bus transfer (PCI initiator read) by PDMAC and PCI read access by G-Bus bus master (B) are
executed simultaneously, any PCI bus access (read or write) is forbidden.
(Any problem doesn’t occur if the number of G-Bus bus master which executes PCI read access simultaneously with
PDMAC is one, or if the G-Bus bus masters execute PCI write access regardless of the number of the G-Bus bus
masters).
Rev. 3.3 May 18, 2007
16-90