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Syscalls (serial communication, ...)

Discuss issues related to Calculator Hacking/Modding.
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Calculators: Casio fx-9750 G II, Casio fx-9860 GII

Re: Syscalls (serial communication, ...)

Postby cakeisalie5 » Thu Apr 13, 2017 10:40 pm

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?
Part of the Planète Casio community (FR) - main author of the P7 project - libp7 - libg1m - FONTCHARACTER reference

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Calculators: Casio fx-7400GII, Casio fx-7400GII (SH4), Casio fx-9750 G II, Casio fx-9750 G II (SH4), Casio fx-9860G, Casio fx-9860 G SD, Casio fx-9860G Slim, Casio fx-9860 GII SD, Casio fx-9860 GII SD Power Graphic 2, Casio Classpad 330 plus, Casio fx-CG 20, Casio Classpad fx-cp400, Casio fx-CG 50

Re: Syscalls (serial communication, ...)

Postby SimonLothar » Fri Apr 14, 2017 7:30 am

cakeisalie5 wrote: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.
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