AN2797 Freescale Semiconductor / Motorola, AN2797 Datasheet - Page 10

• Manufacturer Part Number: AN2797
• Description: Migrating from IBM 750GX to MPC7447A
• Manufacturer: Freescale Semiconductor / Motorola

Feature Overview
The main difference is the fact that the MPC7447A can support 36-bit physical addressing by enabling
HID0[XAEN], thus allowing the increased 64 Gbyte memory space. The extended block size of greater than
256 Mbyte is enabled by asserting HID0[XBSEN] and HID0[HIGH_BAT_EN], and using the extra XBL field in
the upper BAT registers to select larger blocks up to 4Gbyte. The increased area of memory that can be mapped per
BAT means that the programmer does not have to use multiple BATs to map multiple sequential 256 Mbyte blocks
on the MPC7447A.
The other added feature on the MPC7447A is software support for page table searching to offer a custom page table
entry and searching operation if required.
2.5
Both the IBM 750GX and MPC7447A support the 60x bus protocol. The MPC7447A also supports the MPX bus
protocol which is a more efficient protocol based on the 60x implementation.
the IBM 750GX and MPC7447A 60x support.
In addition, the MPC7447A supports an MPX bus mode offering of up to 16 out-of-order transactions, data
streaming, and data intervention for MP systems. These features make the system bus operation much more
efficient, thus increasing the effective bandwidth available in the system. The advantages of the MPX bus can be
found in the MPX Mode section under MPC7447A Added Features.
2.6
The Thermal Assist Unit (TAU) used in the IBM 750GX provides a means of monitoring the junction temperature,
offering an advantage over case or cabinet temperature readings since the die temperature would be very different.
The TAU can operate on a one or two threshold system whereby the threshold values are programmed into one or
two of the TAU’s four special purpose registers. When the temperature reaches one of these thresholds an interrupt
is generated allowing software to take appropriate action to reduce the temperature accordingly.
Instead of the TAU the MPC7447A incorporates a temperature diode that connects to an external temperature
monitor device. These devices are widely available from vendors such as Analog Devices, Maxim and National
Semiconductor. Using the negative temperature coefficient of the diode at a constant current, the monitor device can
determine the junction temperature.
10
IBM 750GX 60x Features
32 bit addressing with 4 bits odd parity
64 bit data bus with 8 bits odd parity, 32 bit data bus
support
Three state MEI cache coherency protocol
L1 and L2 snooping support for cache coherency
Address-only broadcast instruction support
Address pipelining
Support for up to 5 outstanding transactions (one
instruction, four data)
200Mhz maximum bus speed
System Interface
Thermal Assist Unit
Migrating from IBM 750GX to MPC7447A, Rev. 1.0
Figure 6
Table 3. 60x Bus Features
shows how the monitoring device can be connected directly to the
MPC7447A 60x Features
36 bit addressing with 5 bits odd parity
64 bit data bus with 8 bits odd parity
Four state MESI cache coherency protocol
L1 and L2 snooping support for cache coherency
Address-only broadcast instruction support
Address pipelining
Support for up to 16 outstanding transactions
167Mhz maximum bus speed
Table 3
highlights the differences in
Freescale Semiconductor