Question About PASM JMP Instruction

CJMJ

I found this in the documentation example:

jmp #$ 'don't go wandering off, stay here

I'm assuming the JMP is just jumping back to itself, but I can't find the definition for the "#$" address. Does this mean jump to the address on the program counter (PC) [which would be the address of the current instruction]?

Wuerfel_21

CJMJ wrote: »

I found this in the documentation example:

jmp #$ 'don't go wandering off, stay here

I'm assuming the JMP is just jumping back to itself, but I can't find the definition for the "#$" address. Does this mean jump to the address on the program counter (PC) [which would be the address of the current instruction]?

$ is what the assembler thinks the address of the current instruction is.

jrullan

CJMJ wrote: »

I found this in the documentation example:

jmp #$ 'don't go wandering off, stay here

I'm assuming the JMP is just jumping back to itself, but I can't find the definition for the "#$" address. Does this mean jump to the address on the program counter (PC) [which would be the address of the current instruction]?

I recently found the explanation in the Propeller 1 Manual. I recommend that you have it handy until the new manual for Propeller 2 is out.

CJMJ

Yep. There it is, on page 298 in the 1.2 version of the Propeller Manual, "The Here Symbol ‘$’". Totally missed this.
This explanation should definitely be in the P2 manual. Thanks @jrullan.

JonnyMac

You can also use that with an offset. I tried this the other day and it work.

                tjz     x, #$+2                                  ' if x = 0, skip next instruction
                abs     x

This is one way (of many) to accomplish the same outcome. (BTW, I'm not suggesting this is a practical example, it's just to demonstrate you can make adjustments to #$).

Wuerfel_21

and similarly, you can use it to pad to a certain address

        ' pad to 256
        fit 256
        long 0[256-$]

CJMJ

@Wuerfel_21 I understand your use of the 'Here' symbol in your example but I don't understand your example. I actually had to go find the FIT directive in the P1 manual [which is something else needing to make its way into the P2 manual.

Here's how I understand your example: The FIT directive makes sure that all preceding instructions and data does not exceed address 256 but I don't understand exactly what the LONG command is doing. Normally you would use it to fill X number of [LONG] memory locations with some Y value.

CJMJ

@JonnyMac that would be another example of the 'Here" symbol in the P2 manual.

AJL

CJMJ wrote: »

@Wuerfel_21 I understand your use of the 'Here' symbol in your example but I don't understand your example. I actually had to go find the FIT directive in the P1 manual [which is something else needing to make its way into the P2 manual.

Here's how I understand your example: The FIT directive makes sure that all preceding instructions and data does not exceed address 256 but I don't understand exactly what the LONG command is doing. Normally you would use it to fill X number of [LONG] memory locations with some Y value.

Yes: The X number of longs is 256-$, and the Y value is 0.

The fit ensures that you aren't going to generate a negative value in the calculation of 256-$.

Cluso99

Here is another one for you

                      orgh ($ < $400) ? $400 : $              ' set hub >= $400

It is a verilog style command.

If the current hub address is < $400 then set the hub address to $400 else leave it as $ (ie current hub address).
When an orgh $xxx is encountered, pnut zero fills to the new current address (in pasm only code, not sure about spin2). Flexspin also handles this.

evanh

That is handy Cluso. I've had an itch for something like that for a while.

BTW: Verilog most likely borrowed the syntax from C. And given it's not a very C like syntax I'd hazard a guess C borrowed it from an even older language.

ozpropdev

Wuerfel_21 wrote: »

and similarly, you can use it to pad to a certain address

        ' pad to 256
        fit 256
        long 0[256-$]

This can also be achieved usng the ORGF directive

    orgf    256

ozpropdev

JonnyMac wrote: »

You can also use that with an offset. I tried this the other day and it work.

                tjz     x, #$+2                                  ' if x = 0, skip next instruction
                abs     x

This is one way (of many) to accomplish the same outcome. (BTW, I'm not suggesting this is a practical example, it's just to demonstrate you can make adjustments to #$).

Also be aware that when using hubexec the offsets must be scaled for longs.

                tjz     x, #$+2 * 4                              ' if x = 0, skip next instruction
                abs     x

[/code]

kuba

The $ "here" constant is methinks widely used in many assemblers, but I do agree it should be documented somewhere eventually - not everybody using P2 is a veteran