请教：1。C6743片内RAM只有L2可用吗？2 。L1上电之后 默认为Cache模式，搞不懂Cache怎么用？？3 L2是只有128K还是256K吗？手册上写的L2有两段地址，分别是128K的，

cache在dsp的作用，类似于cpu中的缓存。主要是解决CPU（速度快）和内存（速度慢）之间速度不匹配的问题。具体可参考这里：

Why Use Cache
From a DSP application perspective, a large amount of fast on-chip memory
would be ideal. However, over the past years the performance of processors
has improved at a much faster pace than that of memory. As a result, there is
now a performance gap between CPU and memory speed. High-speed
memory is available but consumes much more size and is more expensive
compared with slower memory.
Consider the flat memory architecture shown on the left in Figure 1–1. Both
CPU and internal memory are clocked at 300 MHz such that no memory stalls
occur. However for accesses to the slower external memory, there will be CPU
stalls. If the CPU clock was now increased to 600 MHz, the internal memory
could only service CPU accesses every two CPU cycles and the CPU would
stall for one cycle on every memory access. The penalty would be particularly
large for highly optimized inner loops that may access memory on every cycle.
In this case, the effective CPU processing speed would approach the slower
memory speed. Unfortunately, today’s available memory technology is not
able to keep up with increasing processor speeds, and a same size internal
memory running at the same CPU speed would be far too expensive.