I'm interested in relocatable code, programs that can work independently of the configuration of the EP.

The problem is when you want to make it easily in Basic. RESTORE or ALLOCATE can give you spare memory for your code, but the direction can be different if you have been running another program before or have made immediately a reset.

But if you want the code to work on every EP you must think about relocatable modules.

No, I talk about tiny code with some jumps or calls inside. The Z80 wasn't engineered with relocatable code in mind( except the useful JP(HL) widely used in the EXOS, or the relative jumps, too shorts to be useful).

Then I've though about an easy way to do the trick:

  100 ALLOCATE 20
  110 CODE ORIGEN=HEX$("00,00,00,01,00,02,00,03,00,04,00,05,00,06,00,07,00,08,00,09")
  120 LET CODH=INT(ORIGEN/255)
  130 LET CODL=REM(ORIGEN,255)
  140 FOR A=0 TO 9
  150   READ B,C
  160   LET DIREC=(B*255)+C+ORIGEN
  170   LET H=PEEK(DIREC)
  180   LET L=PEEK(DIREC+1)
  190   LET L=L+CODL
  200   LET H=H+CODH+INT(L/255)
  210   LET L=REM(L,255)
  215   PRINT DIREC,PEEK(DIREC),PEEK(DIREC+1)
  220   POKE DIREC,H
  230   POKE (DIREC+1),L
  240 NEXT A
  250 DATA 0,0,0,2,0,4,0,6,0,8,0,10,0,12,0,14,0,16,0,18
  255 PRINT
  260 FOR A=0 TO 9
  270   PRINT ORIGEN+(A*2),PEEK(ORIGEN+(A*2)),PEEK(ORIGEN+(A*2)+1)
  280 NEXT A

In lines 100-110 we put a test code in the Basic variable memory as usual.
In 120-130 we extract the H and L bytes of the new ORG direction.

Then, in the 140-240 loop we read from DATA in line 250 the absolute directions(ORG=0) we need to relocate .

Then the  content of the memory is compared before and after.

Oh sorry. I'm on holidays without the real thing... no excuses.....Error is my second name....
 
The program fixed:

  100 ALLOCATE 20
  110 CODE ORIGEN=HEX$("00,00,00,01,00,02,00,03,00,04,00,05,00,06,00,07,00,08,00,09")
  120 LET CODH=INT(ORIGEN/256)
  130 LET CODL=REM(ORIGEN,256)
  140 FOR A=0 TO 9
  150   READ B,C
  160   LET DIREC=(B*256)+C+ORIGEN
  170   LET H=PEEK(DIREC)
  180   LET L=PEEK(DIREC+1)
  190   LET L=L+CODL
  200   LET H=H+CODH+INT(L/256)
  210   LET L=REM(L,256)
  215   PRINT DIREC,PEEK(DIREC),PEEK(DIREC+1)
  220   POKE DIREC,H
  230   POKE (DIREC+1),L
  240 NEXT A
  250 DATA 0,0,0,2,0,4,0,6,0,8,0,10,0,12,0,14,0,16,0,18
  255 PRINT
  260 FOR A=0 TO 9
  270   PRINT ORIGEN+(A*2),PEEK(ORIGEN+(A*2)),PEEK(ORIGEN+(A*2)+1)
  280 NEXT A

Thanks Zozo, really your nethod is easy to implement. Only remember, I usually code by hand.....but can do bigger and better things if I begin using an assembler....

Is Turbo Asmon the best?

Ok. And, about the English manual, is it important?

The two if  possible...HEASS and T-ASMON.... Or, can I begin without manuals?

For more serious amounts of machine code, EXOS supports a relocatable file format, so you can do an EXOS call to load a relocatable user program or device driver into an arbitrary block of memory.

zozo: do you know if anyone actually ever used this in practice? It would mean they would have to have a way of producing the bit stream file format. I remember at IS we used to assemble relocatable modules twice, each time with a different ORG (probably 0 and 100h but I can't actually remember) and then we wrote a little utility program that would compare the two files and thus know which bits need to be relocatable, and output the appropriate bit stream file format.

Very interesting idea! Unfortunatelly this utility not published
Now I thinking write similar one

I used the same trick with my very elementary "original" CP/M to EP128 porting: I had the disassembled CP/M BDOS from the Net, I assembled it with ORG 0 and ORG 100h. I wrote a simple python script (running on PC): where the byte values were different I stored the positions inside a table and I used ORG 0 version, so I simply had to add the offset. Since I was about relocating to positions on 256 byte boundaries, I only needed to deal with the high bytes (of course the theory works with even byte granulities, but it needs two tables, as some ops may use only low an and high bytes, and such).

I want to convert a MSX machine code application to Enterprise, it is SETalk, the voice synth.

On MSX it is loaded by a Basic program at a fixed address, but now I want it to work on every Enterprise.

I have been thinking about real relocatable code, not relocatable conversion like it is explained at the beginning on this thread.

---

The real problem I found about doing relocatable code with the Z80 is the impossibility to read the PC register to know the address of the instruction the processor is actually executing.

CALL and JP are the worst instructions to convert to relocatable, but we at least have JP (HL), that eases a lot the conversion.

Also, IS-Basic lets to pass a 16 bit number to the HL register pair on a machine code program created with the command CODE ROUTINE=HEX$("XX","XX", etc), and then the routine called with CALL USR(ROUTINE,ROUTINE)(Thanks Zozo for the tip).

Now we have the start address passed to HL. The routine has been assembled with a ORG 0000h.

SETALK:         PUSH    AF
                PUSH    BC
                PUSH    DE
                PUSH    HL


                CALL    PROG

                POP     HL
                POP     DE
                POP     BC
                POP     AF
                               
I have though that something like this will serve me to do a call:

SETALK:         PUSH    AF
                PUSH    BC
                PUSH    DE
                PUSH    HL          ; is good to store another copy of the start address just in case

                LD      DE, RET1 ; we need the relative address of the return
                PUSH    HL
                ADD      HL, DE
                EXX      DE, HL
                POP      HL
                PUSH    DE          ; Now we have the absolute return address on the stack
                PUSH    HL
                LD      DE,PROG
                ADD      HL,DE
                POP      DE         
                JP      (HL)        ; We still have the start address on DE, but we can
                                    ; pass more data by the stack if we remember to POP it
                                    ; inside the simulated call
                ;CALL    PROG

ret1:           POP     HL
                POP     DE
                POP     BC
                POP     AF
                               

But surely you know an easier way....