Texas Instruments TI89 Developer Guide - Page 77

Chapter 7: Flash Application Layout 35 7.1.3.7. 7.1.3.8. 7.1.4. 7.1.5. 7.1.6. Length of Initial Data Table Number of bytes in initial data table. Optional Header Additional header information may be included after the required header section. The optional header length specifies how many bytes are in the header extension. Relocation Map The OS uses the relocation map to calculate absolute addresses when the positions of the code and data segments are finally established. The relocation map consists of a six-byte entry for each location which needs to be updated. Offset (bytes) 0 3 Length (bytes) 3 3 Contents hole offset base (2 bits) and relative value to place in hole (22 bits) Table 7.4: Relocation Map Format The hole offset specifies where in the application code or initial data table an absolute address needs to be updated. The value to store in the hole is calculated from the base and relative value. The base is 00 for code-segment relative and 10 for data-segment relative. Base values 01 and 11 are reserved for future implementations of AMS. Application Code The code segment contains executable application code and constant data. Initial Data Table When the OS installs an application, it allocates a data segment in RAM to hold static and external variables. The initial data table provides their initial values. Static/external variables which are not explicitly initialized are set to zero. The application's data segment is initialized when the application is installed and reinitialized every time the application is moved in Flash memory because of garbage collection. TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001