Chapter 8: PCI/G-Bus Bridge
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
8-36
8.6.3 TRDY_TIMEOUT
Lock up could occur if the requested PCI Target responds with a
PCI_DEVSEL*
signal, but
does not follow with a
PCI_TRDY
or
PCI_STOP
signal to allow the cycle to complete. To prevent
this, the core provides the programmable
TRDY_TIMEOUT
timer to determine the point at
which the Master will abandon the cycle. This register, which is at configuration address
0x40, contains a value that is the number of PCI clocks to allow before generating a timeout.
The default value for the register is 0x80, which is well in excess of the PCI 2.1 requirement
for new devices. A write of “0” to the
TRDY_TIMEOUT
register disables this function so it can
be used with any non-compliant legacy devices that may require more time to return a
PCI_TRDY
or
PCI_STOP
signal.
8.6.4 RETRY_TIMEOUT
The second case for which the core includes a timeout register is the case for which the PCI
Target device retries beyond the retry count. To prevent this, the core provides the
programmable
RETRY_TIMEOUT
register whose value sets the number of retries that the core
will perform as a Master before abandoning a cycle. This register is at configuration address
0x41. The default value for the register is 0x80, which is well in excess of the PCI 2.1
requirement for new devices. A write of “0” to the
RETRY_TIMEOUT
register disables this
function, so it can be used with any non-compliant legacy devices that may execute more
retries.
8.6.5 PCI Target Delayed Read Handling
The core considers a Target Read to be a Delayed Read if the application has not returned
data within 16 PCI clock cycles. In this case, the core will issue a PCI bus retry and
automatically lock out all other Target Read requests until the application has returned the
data and the original requestor has returned to read it. If after 2
15
PCI clocks the original
requestor has not returned to read the data, the core aborts the lockout of Target Read
requests and discards the Delayed Read cycle.
Target Writes are still allowed during a Delayed Read.
Summary of Contents for TMPR7901
Page 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Page 14: ...Handling Precautions ...
Page 15: ......
Page 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Page 41: ...4 Precautions and Usage Considerations 4 2 ...
Page 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
Page 43: ......
Page 259: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 1 13 Removed ...
Page 260: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 2 ...