The latency plot of any SoC device usually has n plateaus, if there are n levels to reach the external memory after all the cache boundaries.
The Y-axis is in nano seconds (ns) and the X-axis is in KiloBytes (KB).
In the TDA2xx and TDA2ex device, there are 2 levels of cache (L1, L2) and then the external memory is on the L3. From the latency plot, you can find out how many levels of cache an SoC has and what are their approximate cache sizes; from the plot, you can see that there are 3 plateaus.
L1 plateau ends by ~32 KB (cache size)
L2 plateau ends by ~2 MB (cache size)
L3 plateau starts after 2MB (L2) and the peak of saturation at DDR2 latency.
The DDR2 latency is very high due to the limitation mentioned in Section 2.4.2.