Syscalls (serial communication, ...)

[cakeisalie5 Profile Website]

Found this today online, and as you told me OHP was only possible on USB, I'm quite surprised... is there any way to do OHP on serial?

[SimonLothar]

Found this today online, and as you told me OHP was only possible on USB, I'm quite surprised... is there any way to do OHP on serial?

They swapped the physical port order on the PCB with the fx-9860GII types. The calculator pictured here is a fx-9860G connected via USB to a OH 9860.

But indeed I see some possibilities to do OHP via the serial port:
1. OS enhancement.
The OS enhancement will be reliable but not widely accepted by the customers. Can be a very complicated process to achieve.
2. some persistent timer.
I did some experiments with persistent timers long ago. At present I do not know, if there is some persistent timer available with the actual OSes.
3. the UBC.
I use the UBC to redirect processing (an spool information via the serial port out of the redirection code) since years. I did it even with the fx-CG50 recently. It is more complicated with SH-3 calculators because they do not have the DBR.
4. With the above mentioned UBC-tool on SH-3 calculators I switched the interrupt-table to RAM (VBR) to redirect the UBC-interrupt-handler. Perhaps it is possible to abuse some other interrupt-handler, too.

In the latter three cases you have to find some unused area in RAM. This usually is OS-dependent. And - of course - there mustn't be another application which claims the same unused RAM area.