| XScale Display Controller vs. StrongARM
The display controller in the XScale processor has a number of differences from the StrongARM.
Deeper Input FIFO
The most notable is that the input FIFO is much deeper, effectively eliminating the flicker issues that the StrongARM exhibited under certain bus loading conditions (details).
ADS still generally recommends 8/12 bpp mode for larger displays, as it requires half the memory bus bandwidth of 16 bpp. However, 16 bpp mode is much improved on the XScale.
Reduced Flexibility in Pixel Clock Rate
The XScale pixel clock comes from dividing the 100MHz memory clock by (2,4,6,...), while the StrongARM divided down its 206MHz CPU clock by (6,8,10,...). Although the XScale can achieve higher clock rates (50 MHz vs. 34), it has higher granularity between steps.
This issue is most apparent for panels that need pixel clock rates in the 10-35 MHz range. While the StrongARM can generate eight clock rates within this range (34, 26, 21, 17, 15, 13, 11.5 and 10.3 MHz), the XScale can generate only four (25, 17, 12.5 and 10 MHz). This gives less flexibility when trading off bus bandwidth for display performance.
Driver and Cable Changes
There are two key changes that you'll need to know about if you are transitioning from StrongARM to XScale:
- Cables for Active Panels
The XScale no longer remaps the display signals for active panels between 12 and 16 bpp modes. That means that you only need one cable.
When updating to an XScale system, you will only need a new cable if you are currently using a 12-bit cable with an active display on your StrongARM system.
See Topic 1202 for the display cable drawings used on XScale and StrongARM development systems.
- Different Display Timings
The XScale display controller uses different registers to configure the display controller. At this time, you'll need to send your display to ADS for configuration and test if it's not on the list of supported displays at topic 211.
Transitioning Your Display to XScale
Please contact our Sales Group if you are converting from an ADS StrongARM product. We can work with you to transition the display in your product to the XScale.
For further reading about displays on our products, see the Display topic index.
Edited by akidder 27-Aug-2003: Add paragraph about XScale pixel clock.
Edited by akidder 13-Jul-2004: Add link to topic 1202 for cable drawings