Difference between revisions of "Geneve GPL Interpreter"
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For different speeds different kinds of RAM (DRAM vs. SRAM) are used. The ROMPAGE feature sets the 4000-5FFF page value to >BA, which points to the address space of the peripheral card in the box, unlike >07 which contains the MDOS replacement DSR. | For different speeds different kinds of RAM (DRAM vs. SRAM) are used. The ROMPAGE feature sets the 4000-5FFF page value to >BA, which points to the address space of the peripheral card in the box, unlike >07 which contains the MDOS replacement DSR. | ||
The | The cartridge ROM (6000-7FFF) is always mapped to page 36, while the second ROM page is 37. The GROM pages are 38-3F. Page 03 must be mapped to C000 at all times to enable cartridge access. | ||
== Speed selection == | == Speed selection == | ||
Revision as of 00:57, 17 November 2019
Mapping
For Speed 5 and MDOS DSR:
| Page for 0000-1FFF | Page for 2000-3FFF | Page for 4000-5FFF | Page for 6000-7FFF | Page for 8000-9FFF | Page for A000-BFFF | Page for C000-DFFF | Page for E000-FFFF |
|---|---|---|---|---|---|---|---|
| EC | ED | 07 | 36 | EE | EF | 03 | 35 |
For different speeds different kinds of RAM (DRAM vs. SRAM) are used. The ROMPAGE feature sets the 4000-5FFF page value to >BA, which points to the address space of the peripheral card in the box, unlike >07 which contains the MDOS replacement DSR.
The cartridge ROM (6000-7FFF) is always mapped to page 36, while the second ROM page is 37. The GROM pages are 38-3F. Page 03 must be mapped to C000 at all times to enable cartridge access.
Speed selection
The GPL Interpreter allows for selecting the execution speed. Five speeds are selectable. The speed is determined by these settings:
| Speed | Video waitstates | Extra waitstates | Page for 0000-1FFF | Page for 8000-9FFF |
|---|---|---|---|---|
| 1 | x | x | EC | 34 |
| 2 | x | - | 33 | 34 |
| 3 | x | - | EC | 34 |
| 4 | x | - | 33 | EE |
| 5 | x | - | EC | EE |
The memory pages EC, ED, EE, and EF are SRAM pages with 0 waitstate access. Other pages are DRAM pages with one waitstate. Thus, the speed is controlled by waitstates in the GPL interpreter (locations 0000-1FFF) and in the PAD RAM (8300-83FF), which is not the high speed on-chip RAM of the TMS9995 processor (which is always located at F000, regardless of the mapper value).