Which calculators run RPL under the hood?

[Christoph Giesselink]

(11-30-2019 04:22 AM)rprosperi Wrote:  But I still would like to know why, with the RPL system available, HP would choose to build all the lower-end machines from scratch. Was saving a little ROM and RAM in those models really less expensive than writing and testing code for those same models from scratch? It's hard to compare these economics today with the huge drop in price of hardware and always rising price of software development.

I don't think that everything was build from scratch. The special Saturn CPU architecture was introduced with the 71B in this case with floating point math IEEE 754-1985 Standard. I don't know the hardware follower 18C, but the next calculator, the 28C uses BCD math. The basic math functions inside are written in Saturn assembler. There's somehow a misunderstanding of RPL. With RPL you have no access to the hardware. You cannot read or write to CPU registers or other peripherals like the LCD display with RPL directly. This could only be done by the CPU executing binary code. So all basic function of an RPL machine are written in assembler, but - with an interface for the RPL interpreter mostly implemented as PCO (Primitive Code Object). The other possibility is using a RPL object and embedding assembler code inside with a =DOCODE object. So all the basics with hardware reference are already written in assembler.

Some words about speed and memory. I massively expanded the entry-point list of the HP28S primary created by J-F and created an entry point list for the 28C rev. 1CC. Therefore I compared the implementations with the HP48SX rev.E. When you have the luck like me having parts of the HP48SX rev.E source code, you see that the HP48SX sources directly build from the HP28S sources and this one from the 28C. Even more, the HP48SX rev.E source sometimes contain disabled code from the HP28S and the code replacement directly in front or behind the disabled code. And there you find replacements from assembler to RPL for saving memory and from RPL to assembler to save time.

Another interesting find was a routine, I think it was assembler code, doing the same thing on the HP28S and on the HP42S but implemented in different ways. What a waste.

I know that HP began from scratch for the HP10BII and HP17BII+ calculators. Here both calculators use basic mathematical routines written in C.