User`s manual

32 rabbit.com Rabbit Memory Organization

5.3.2.1 Compiling to RAM

For RAM compiles, all banks (quadrants) are mapped to RAM. In a 20-bit physical address space (i.e.,

1 MB physical address space), a 512 KB memory would be mapped with the lower 256 KB mapped to

banks 0 and 2. The higher 256 KB are mapped to banks 1 and 3. In this configuration, A16 is inverted to

provide access to the constants and data starting at the 64K boundary. The standard configuration is to set

the SEGSIZE register to 0xDD so that the base segment occupies the entire 52 KB region up to the stack

segment. Note that this configuration causes the DATASEG register to be irrelevant.

The BIOS sets the MMIDR to 0x21. Bit 5 of this register enables the instruction/data split and bit 0 causes

the inversion of A16.

Figure 5-4 RAM Compile Memory Mapping

Instruction

Data

Shared

0x00000

0x03000

0x0D000

0x10000

0x13000

0x1D000

Root Code

Xmem Code

Root Constants

Root Data

Xmem Code

continued,

xalloc, Stacks

RAM

Root Code

Root Data

Constants

Xmem

Stack

0xD000

0xE000

0xFFFF

0x0000

0x3000

0xCFFF

0x3000

0x0000

MECR = 0x0

MMIDR = 0x21

SEGSIZE = 0xDD

DATASEG = 0x0 (irrelevant)

0xFFFFF