What does “jmp *” mean in 6502 assembly?

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Right now I am learning 6502 assembly. Currently I am using the MADS assembler to program for the Atari 800. This program is just a small tutorial program that came with the assembler zip file I downloaded. The only piece of this program I did't understand is the jmp * operation, what does the '*' mean? Full program:

sm_ptr = $58
ch = $2f4 
chr = $2400 
rom_chr = $e000 
org $2000
.proc main 
mva #>chr ch 
ldx #0 
copy_loop
mva rom_chr,x chr,x
mva rom_chr+$100,x chr+$100,x
mva rom_chr+$200,x chr+$200,x
mva rom_chr+$300,x chr+$300,x
inx
bne copy_loop
ldx #0 
space_loop
mva charset.space,x chr,x
inx
cpx #8
bne space_loop 
ldy #0 
loop 
tya
sta (sm_ptr),y
iny
bne loop
jmp *
.local charset
space 
.byte %01000100 
.byte %00101000
.byte %01111100
.byte %01010100
.byte %11111110
.byte %10101010
.byte %10111010
.byte %00000000
.endl
.endp 
run main

assembly 6502 atari-800

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edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

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up vote
1
down vote

favorite

Right now I am learning 6502 assembly. Currently I am using the MADS assembler to program for the Atari 800. This program is just a small tutorial program that came with the assembler zip file I downloaded. The only piece of this program I did't understand is the jmp * operation, what does the '*' mean? Full program:

sm_ptr = $58
ch = $2f4 
chr = $2400 
rom_chr = $e000 
org $2000
.proc main 
mva #>chr ch 
ldx #0 
copy_loop
mva rom_chr,x chr,x
mva rom_chr+$100,x chr+$100,x
mva rom_chr+$200,x chr+$200,x
mva rom_chr+$300,x chr+$300,x
inx
bne copy_loop
ldx #0 
space_loop
mva charset.space,x chr,x
inx
cpx #8
bne space_loop 
ldy #0 
loop 
tya
sta (sm_ptr),y
iny
bne loop
jmp *
.local charset
space 
.byte %01000100 
.byte %00101000
.byte %01111100
.byte %01010100
.byte %11111110
.byte %10101010
.byte %10111010
.byte %00000000
.endl
.endp 
run main

assembly 6502 atari-800

share|improve this question

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

asked 4 hours ago

user115898

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

up vote
1
down vote

favorite

up vote
1
down vote

favorite

Right now I am learning 6502 assembly. Currently I am using the MADS assembler to program for the Atari 800. This program is just a small tutorial program that came with the assembler zip file I downloaded. The only piece of this program I did't understand is the jmp * operation, what does the '*' mean? Full program:

sm_ptr = $58
ch = $2f4 
chr = $2400 
rom_chr = $e000 
org $2000
.proc main 
mva #>chr ch 
ldx #0 
copy_loop
mva rom_chr,x chr,x
mva rom_chr+$100,x chr+$100,x
mva rom_chr+$200,x chr+$200,x
mva rom_chr+$300,x chr+$300,x
inx
bne copy_loop
ldx #0 
space_loop
mva charset.space,x chr,x
inx
cpx #8
bne space_loop 
ldy #0 
loop 
tya
sta (sm_ptr),y
iny
bne loop
jmp *
.local charset
space 
.byte %01000100 
.byte %00101000
.byte %01111100
.byte %01010100
.byte %11111110
.byte %10101010
.byte %10111010
.byte %00000000
.endl
.endp 
run main

assembly 6502 atari-800

share|improve this question

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

asked 4 hours ago

user115898

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

Right now I am learning 6502 assembly. Currently I am using the MADS assembler to program for the Atari 800. This program is just a small tutorial program that came with the assembler zip file I downloaded. The only piece of this program I did't understand is the jmp * operation, what does the '*' mean? Full program:

sm_ptr = $58
ch = $2f4 
chr = $2400 
rom_chr = $e000 
org $2000
.proc main 
mva #>chr ch 
ldx #0 
copy_loop
mva rom_chr,x chr,x
mva rom_chr+$100,x chr+$100,x
mva rom_chr+$200,x chr+$200,x
mva rom_chr+$300,x chr+$300,x
inx
bne copy_loop
ldx #0 
space_loop
mva charset.space,x chr,x
inx
cpx #8
bne space_loop 
ldy #0 
loop 
tya
sta (sm_ptr),y
iny
bne loop
jmp *
.local charset
space 
.byte %01000100 
.byte %00101000
.byte %01111100
.byte %01010100
.byte %11111110
.byte %10101010
.byte %10111010
.byte %00000000
.endl
.endp 
run main

assembly 6502 atari-800

assembly 6502 atari-800

share|improve this question

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

asked 4 hours ago

user115898

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

asked 4 hours ago

user115898

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

share|improve this question

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

edited 3 hours ago

Brian Tompsett - 汤莱恩

573212

573212

asked 4 hours ago

user115898

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 4 hours ago

user115898

476

asked 4 hours ago

user115898

476

476

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

New contributor

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

user115898 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

add a comment | 

2 Answers
2

active

oldest

votes

up vote
4
down vote



accepted

MADS uses * in three ways (See MADS "Manual")

• Using the current assembly address for calculation of an address, i.e. the one the actual statement is assembled to.


• Multiplying in expressions.


• Mark the beginning of a comment (until line end)

In above listing it will be interpreted as the address the JMP instruction is assembled to, so it will form an infinite loop, effectively halting the machine until Reset.

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

add a comment | 

up vote
3
down vote

I suspect the * means the current instruction/location, as it does in some other assemblers, like PDP-8.  Often it would be used in an expression like *-label in the data section to get something's size, or *+3 perhaps, in code.

If that's the case for 6502 assembly, then jmp * means branch to self, or, infinite loop, which would be a form of halting the program.

This makes some sense as it comes at the end of main, which presumably has nothing to return to for a bare metal program.

Some assemblers (e.g. masm, Microsoft's x86 assembler) use $ for the same meaning.

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

• 
  
  
  

  
  

  
  
  
  
  
  

  
  It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
  – user115898
  4 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Thanks, it is correct that it is an infinite loop that just loops back the the same line.
  – user115898
  4 hours ago
  

  
  
  
  

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
4
down vote



accepted

MADS uses * in three ways (See MADS "Manual")

• Using the current assembly address for calculation of an address, i.e. the one the actual statement is assembled to.


• Multiplying in expressions.


• Mark the beginning of a comment (until line end)

In above listing it will be interpreted as the address the JMP instruction is assembled to, so it will form an infinite loop, effectively halting the machine until Reset.

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

add a comment | 

up vote
4
down vote



accepted

MADS uses * in three ways (See MADS "Manual")

• Using the current assembly address for calculation of an address, i.e. the one the actual statement is assembled to.


• Multiplying in expressions.


• Mark the beginning of a comment (until line end)

In above listing it will be interpreted as the address the JMP instruction is assembled to, so it will form an infinite loop, effectively halting the machine until Reset.

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

add a comment | 

up vote
4
down vote



accepted

up vote
4
down vote



accepted

MADS uses * in three ways (See MADS "Manual")

• Using the current assembly address for calculation of an address, i.e. the one the actual statement is assembled to.


• Multiplying in expressions.


• Mark the beginning of a comment (until line end)

In above listing it will be interpreted as the address the JMP instruction is assembled to, so it will form an infinite loop, effectively halting the machine until Reset.

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

MADS uses * in three ways (See MADS "Manual")

• Using the current assembly address for calculation of an address, i.e. the one the actual statement is assembled to.


• Multiplying in expressions.


• Mark the beginning of a comment (until line end)

In above listing it will be interpreted as the address the JMP instruction is assembled to, so it will form an infinite loop, effectively halting the machine until Reset.

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

share|improve this answer

share|improve this answer

edited 3 hours ago

Michael Kjörling

1,3811825

edited 3 hours ago

Michael Kjörling

1,3811825

edited 3 hours ago

Michael Kjörling

1,3811825

1,3811825

answered 3 hours ago

Raffzahn

38.1k485153

answered 3 hours ago

Raffzahn

38.1k485153

answered 3 hours ago

Raffzahn

38.1k485153

38.1k485153

add a comment | 

add a comment | 

up vote
3
down vote

I suspect the * means the current instruction/location, as it does in some other assemblers, like PDP-8.  Often it would be used in an expression like *-label in the data section to get something's size, or *+3 perhaps, in code.

If that's the case for 6502 assembly, then jmp * means branch to self, or, infinite loop, which would be a form of halting the program.

This makes some sense as it comes at the end of main, which presumably has nothing to return to for a bare metal program.

Some assemblers (e.g. masm, Microsoft's x86 assembler) use $ for the same meaning.

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

• 
  
  
  

  
  

  
  
  
  
  
  

  
  It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
  – user115898
  4 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Thanks, it is correct that it is an infinite loop that just loops back the the same line.
  – user115898
  4 hours ago
  

  
  
  
  

add a comment | 

up vote
3
down vote

I suspect the * means the current instruction/location, as it does in some other assemblers, like PDP-8.  Often it would be used in an expression like *-label in the data section to get something's size, or *+3 perhaps, in code.

If that's the case for 6502 assembly, then jmp * means branch to self, or, infinite loop, which would be a form of halting the program.

This makes some sense as it comes at the end of main, which presumably has nothing to return to for a bare metal program.

Some assemblers (e.g. masm, Microsoft's x86 assembler) use $ for the same meaning.

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

• 
  
  
  

  
  

  
  
  
  
  
  

  
  It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
  – user115898
  4 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Thanks, it is correct that it is an infinite loop that just loops back the the same line.
  – user115898
  4 hours ago
  

  
  
  
  

add a comment | 

up vote
3
down vote

up vote
3
down vote

I suspect the * means the current instruction/location, as it does in some other assemblers, like PDP-8.  Often it would be used in an expression like *-label in the data section to get something's size, or *+3 perhaps, in code.

If that's the case for 6502 assembly, then jmp * means branch to self, or, infinite loop, which would be a form of halting the program.

This makes some sense as it comes at the end of main, which presumably has nothing to return to for a bare metal program.

Some assemblers (e.g. masm, Microsoft's x86 assembler) use $ for the same meaning.

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

I suspect the * means the current instruction/location, as it does in some other assemblers, like PDP-8.  Often it would be used in an expression like *-label in the data section to get something's size, or *+3 perhaps, in code.

If that's the case for 6502 assembly, then jmp * means branch to self, or, infinite loop, which would be a form of halting the program.

This makes some sense as it comes at the end of main, which presumably has nothing to return to for a bare metal program.

Some assemblers (e.g. masm, Microsoft's x86 assembler) use $ for the same meaning.

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

share|improve this answer

share|improve this answer

answered 4 hours ago

Erik Eidt

882311

answered 4 hours ago

Erik Eidt

882311

answered 4 hours ago

Erik Eidt

882311

882311

• 
  
  
  

  
  

  
  
  
  
  
  

  
  It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
  – user115898
  4 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Thanks, it is correct that it is an infinite loop that just loops back the the same line.
  – user115898
  4 hours ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
  – user115898
  4 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  Thanks, it is correct that it is an infinite loop that just loops back the the same line.
  – user115898
  4 hours ago
  

  
  
  
  

It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
– user115898
4 hours ago

It could, it doesn't seem to effect the main program. I'll test that hypothesis right now.
– user115898
4 hours ago

Thanks, it is correct that it is an infinite loop that just loops back the the same line.
– user115898
4 hours ago

Thanks, it is correct that it is an infinite loop that just loops back the the same line.
– user115898
4 hours ago

add a comment | 

user115898 is a new contributor. Be nice, and check out our Code of Conduct.

 

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