Therefore if you patch CPM you need to:
- * ensure the RAM selection state is as expected- * the upper ROM is enabled and AMSDOS ROM is selected (this can be done using firmware functions to get the current rom state and number and restore it).- * avoid touching AMSDOS/firmware areas unless you are also patching it.- * restore the alternative registers if you modify them.
The lower firmware jumpblock exists at &0000-&0040 because it is needed by the firmware jumpblock to call into the OS rom. The following changes are made for CP/M 2.2: