Zxdb supports the following commands for dealing with assembly language:
disassemble / di: Disassemble at the current location (or a given location)
nexti / ni: Step to the next instruction, stepping over function calls.
stepi / si: Step the next instruction, following function calls.
regs: Get the CPU registers.
zxdb maintains information about whether the last command was an assembly command or a source-code and will show that information on stepping or breakpoint hits. To switch to assembly-language mode, type disassemble, and to switch back to source-code mode, type list.
