SKCTL bits 4-6. Sound generation?

[Synthpopalooza]

So I found this on the Altirra hardware manual:

 

Can this be used for sound generation on it's own?  I.E. make like we're sending data to the SIO, but channels 3 and 4 pick up the data and transmit audible sound?  Maybe a means of generating samples?

Edited May 26, 2021 by Synthpopalooza

[phaeron]

Not really.

 

No for sending to SIO, since in that case the timers are driving the serial port. There's no feedback from the serial port to the timer or audio circuits, except for the one case of two-tone mode -- and that case is limited by start/stop bits in the mix.

 

For receiving, asynchronous mode allows you to gate-enable timers 3 and 4 to only run when receiving a byte. However, for this to work you need to receive a byte, and there is no built-in capability in the computer for loopback. Thus, short of cooperation with an external device, the only use for this mode is as a manual gate to stop those timers on demand. If you do receive a byte from a device, the timers just run for 19 ticks regardless of the data byte received.

 

The external clock is probably the most potentially useful, but also requires an external device to drive the clock lines. The most common devices that can do this are probably the MIDIMate and the Indus GT. In the latter case, it's of dubious use as you could just have the Indus GT make the sound instead via its audio capability.

 

In theory, you could use dummy writes to SEROUT to trigger the serial output complete interrupt on a programmable delay. It's potentially faster than other methods as it's the only IRQ that automatically deasserts instead of needing IRQST bits toggled, but it's still a struggle to find a use for it.

 

[tschak909]

Fujinet can also emit an external clock, as well.

-Thom