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RPi 4 / STM32 / ESP32 / Teensy 4 / RISC-V GAZPACHO

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brucehoult:
That's just insane.

Nominal Animal:
Technically, gcc/cc1/g++ and gas/gdb/objdump are different packages in the same toolchain, which explains why sometimes gdb/objdump disagree with gcc what the binary code actually is.

Nevertheless, that is an obvious bug in binutils-gdb, and should be reported to the bugzilla with reproducible examples.

That said, bugs #10288 and #10924 have been open since 2009, and are about ARM7TDMI instruction decoding.  It looks like nobody cared enough to do it properly.  Most likely, companies used just enough resources to get support into GCC, and let the users worry about the rest of the toolchain.

GeorgeOfTheJungle:
I had never seen a µC do a jmp in zero cycles before.  :-+


--- Code: ---while (1) *toggle= mask;
--- End code ---

How fast can those longan RISC-Vs toggle a gpio? 1/4th the µC clock? 10MHz was the max I could get on a esp32@240MHz.

SiliconWizard:

--- Quote from: GeorgeOfTheJungle on November 25, 2019, 06:51:58 pm ---I had never seen a µC do a jmp in zero cycles before.  :-+


--- Code: ---while (1) *toggle= mask;
--- End code ---

--- End quote ---

Whereas I'm not sure there were any "MCU" per se that had this, there were certainly CPUs in general that could loop with zero overhead, using some kind of "REP" prefix instruction. Not exactly a general "jmp" of course, but could still be used for many things.
(Don't some of the Microchip PICs have something like this in their instruction set? Maybe the dsPIC?)

coppice:

--- Quote from: GeorgeOfTheJungle on November 25, 2019, 06:51:58 pm ---I had never seen a µC do a jmp in zero cycles before.  :-+

--- End quote ---
There have been some DSP oriented controller cores which offered zero cycle loop overhead, just like most full on DSP cores.

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