ESP32 Forum

Hi,
chip: esp32-U4WDH
IDF version:v4.4 with commit 8153bfe412
platform: vscode on linux
description:
Need low latency gpio interrupt, so wrote the following code in assembly to test the feasibility. ETS_GPIO_INTR_SOURCE is linked to number 31 of the interrupt matrix using intr_matrix_set(). The triggering mode is GPIO_INTR_NEGEDGE. The isr is on level5 using xt_highint5. The isr simply toggles gpio13 once.
Bluetooth has been disabled and CONFIG_ESP_SYSTEM_CHECK_INT_LEVEL is set to 4.
problem:
The isr is triggered by desired condition and voltage toggle is observed using oscilloscope, but program crashes due to interrupt wdt timeout on core0. The followings are backtrace infos and detailed coredump is in the attachment:
The assembly codes are the followings:
After reading some posts on this forum, it feels like freeRtos isr that feeds the wdt is kinda blocked and interrupt wdt is never fed once the level5 isr is triggered.
Digging into the backtrace, it shows that "waiti 0" command somehow causes the problem.
Any hint on the reason and possible fixes?

Thanks & Regards
wxd

Typo?

Code: Select all

movi    a12, GPIO_OUT_W1TS_REG
...
s32i    a15, a12, 0

a12 isn't saved/restored. Guess you meant to use a14 instead.

Dear MicroController,

Thanks a lot for the reply, thought the topic has sunk. Using a14 to store gpio address for further toggling is indeed what should've been done and I will make the correction.
Besides this, since I am not familiar with using assembly language and the code's frame was adopted from certain posts written by some experienced guys, may I ask a question about saving and restoing the register values at the beginning of this code? e.g. saving a13, a14, a15 means I can only use these 3 registers in the following assembly routine while all other registers' value must remain unchanged, otherwise the program cannot be restored to its former state before entering isr, and to use other registers(if it is possible), I must save their values first and restore them just like the thing that is done to a13, a14, a15. Is this the basic concept isr in assembly should stick to? Really appreciate it if you could give a rough guidance.

Best regards
wxd

You're welcome

Yes, your understanding is exactly correct: When the ISR returns, all registers must contain the value they had when the ISR was entered. The original content of all registers used/'clobbered' by the ISR needs to be saved to some location in RAM and loaded back before exiting the ISR. Failure to do so can have absolutely any consequences in terms of erroneous behaviour of the application, and the problems tend to be completely unpredictable and non-deterministic because the state of the program/CPU right before entering the ISR usually is, and consequently so is the thing that will break.

You can use any and all registers you want in an ISR, as long as you save and restore them before returning. Primarily, these are the 'general purpose' a0...a15 registers, but other CPU state may need to be added to the list, like for example the 'shift-amount register' (SAR) if the ISR does a 'dynamic' shift (like "1 << some_variable" in C).