[hatari-devel] DSP and HREQ

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Hello

while looking at the level 6 interrupt ttat the DSP can trigger, I 
wonder if everything is emulated.

From the DSP user manual, HREQ is set in non DMA mode when RXDF and/or 
TXDE are set, and HREQ is cleared when both RXDF and TXDE are cleared 
(this requires TREQ and RREQ to be set in the ICR)

In Hatari, the status of HREQ is maintained in the function 
dsp_core_hostport_update_hreq().

When HREQ becomes 1, it calls DSP_TriggerHostInterrupt which sets 
bDspHostInterruptPending=true and creates a pending level 6 interrupt.

But what happens when HREQ becomes 0 at the dsp side ? From the current 
code, it seems bDspHostInterruptPending will remain true and the level 6 
interrupt remains pending ?
Is this really the case on a real Falcon ? I can't test it myself, but I 
guess it should set bDspHostInterruptPending=false and cancel the 
pending DSP's level 6 int.

Can someone test this on his falcon ? (Maybe doug already encountered 
this ?)

For example :

test 1 :

 - set SR=2500 at the cpu side
 - have the DSP set HREQ=1 (by transferring data)
 - we should get a level 6 interrupt at the cpu side, that will call by 
default exception number $F (at address $3c)

In the interrupt handler :
 - If we read ISR, is bit 7 set to 1 ?
 - If we then read the low byte of receive or transmit register, this 
should clear ISR. Is ISR bit 7 set to 0 after a read ?



test 2 to test when hreq goes back to 0 :

 - set SR=2700 at the cpu side
 - have the DSP set HREQ=1 (by transferring data)
 - poll ISR to see when HREQ=1 in bit 7
 - when HREQ=1 in bit 7, read the low byte of receive or transmit register
 - wait for HREQ to become 0 in bit 7 (should be immediate after the 
read above I guess)
 - set SR=2500 : nothing shuold happen, level 6 interrupt at $3c should 
not be called.


Nicolas