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speculatrix
PostPosted: Fri Apr 22, 2022 7:13 am 
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Coincidentally, I’ve just been grappling with something similar. Although my skills here are basic, I have documented what I did here: https://mansfield-devine.com/speculatri ... ng-system/

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BigEd
PostPosted: Fri Apr 22, 2022 7:36 am 
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Location: England
Ah, thanks, I see now!
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Andre
PostPosted: Fri Apr 22, 2022 11:45 am 
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Posts: 21
Location: Brisbane Australia
Hi

Spotted an error if anybody was looking closely.

Quote:
...yes it was a 10ms timer interrupt
JMP ($04F0) ; jump to vector1 interrupt
_vector1_return:
INC SYSTEM_TIMER
CLC
LDA SYSTEM_TIMER
CMP #$64 ; HAS TIMER REACHED 100 (0x64)
BCC _exit_irq
LDA #$00
STA SYSTEM_TIMER
INC SYSTEM_SECONDS

JMP ($04F2) ; jump to vector2 interrupt
_vector2_return:
_not_via:

JMP ($04F4) ; jump to vector3 interrupt
_vector3_return:
_exit_irq:
PLA
PLX
PLY

_irq_last_byte_address:
RTI ; Return from IRQ interrupt


the line BCC _exit_irq should be a BCC to _not_via
otherwise the JMP(indirect) for vector3 will be missed.

This is still all work in progress so testing is limited.

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Andre
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BigDumbDinosaur
PostPosted: Fri Apr 22, 2022 3:45 pm 
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Posts: 8182
Location: Midwestern USA
Andre wrote:
Code:
...yes it was a 10ms timer interrupt
JMP ($04F0) ; jump to vector1 interrupt
_vector1_return:
INC SYSTEM_TIMER
CLC
LDA SYSTEM_TIMER
CMP #$64 ; HAS TIMER REACHED 100 (0x64)
BCC _exit_irq
LDA #$00
STA SYSTEM_TIMER
INC SYSTEM_SECONDS

JMP ($04F2) ; jump to vector2 interrupt
_vector2_return:
_not_via:

JMP ($04F4) ; jump to vector3 interrupt
_vector3_return:
_exit_irq:
PLA
PLX
PLY

_irq_last_byte_address:
RTI ; Return from IRQ interrupt

Surrounding your code snippets with code brackets will make it a little easier to read.

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teamtempest
PostPosted: Sat Apr 23, 2022 2:35 pm 
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Joined: Sun Nov 08, 2009 1:56 am
Posts: 388
Location: Minnesota
Code:
...yes it was a 10ms timer interrupt
JMP ($04F0) ; jump to vector1 interrupt
_vector1_return:
INC SYSTEM_TIMER
CLC
LDA SYSTEM_TIMER
CMP #$64 ; HAS TIMER REACHED 100 (0x64)
BCC _exit_irq
LDA #$00
STA SYSTEM_TIMER
INC SYSTEM_SECONDS


An alternative might be to count down instead of up:

Code:
JMP ($04F0)
_vector1_return:
DEC SYSTEM_TIMER
BNE _exit_irq
INC SYSTEM_SECONDS
LDA #100
STA SYSTEM_TIMER
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Sheep64
PostPosted: Tue Jun 14, 2022 11:55 am 
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Joined: Tue Aug 11, 2020 3:45 am
Posts: 311
Location: A magnetic field
Andre on Fri 22 Apr 2022 wrote:
Code:
_exit_irq:
PLA
PLX
PLY


That is an unusual order. On NMOS 6502, PHA // TXA // PHA // TYA // PHA is traditional. On 65C02, this can be compacted to PHA // PHX // PHY and would be reversed with PLY // PLX // PLA. Unless the IRQ handler begins with PHY // PHX // PHA, the software running outside of interrupt will have its register contents shuffled.

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