i2c_master: Shorted SDA/SCL lines cause a watchdog timeout (IDFGH-12586)

[KJ7LNW]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

IDF version.

5a40bb8

Espressif SoC revision.

ESP32-C6

Operating System used.

Linux

How did you build your project?

Command line with CMake

If you are using Windows, please specify command line type.

None

Development Kit.

ESP32-WROOM-32

Power Supply used.

USB

What is the expected behavior?

Return a timeout or ESP_ERR_INVALID_STATE when there is a bus failure.

What is the actual behavior?

The device hangs and triggers an ISR WDT

Steps to reproduce.

1. Continuously sample the I2C bus with i2c_master_transmit_receive
2. Short the SDA and SCL pins together with a 2.1kOhm resistor. (I know, this is not advised, but we want the product to be as robust as possible).

Debug Logs.

(note: these backtrace lines might be off by a line or two due to debug prints I had added to i2c_master.c)

Guru Meditation Error: Core  0 panic'ed (Interrupt wdt timeout on CPU0). 

Core  0 register dump:
MEPC    : 0x40803702  RA      : 0x408038fe  SP      : 0x4080d240  GP      : 0x4080b8a4  
Stack dump detected
0x40803702: i2c_ll_is_bus_busy at /home/ewheeler/src/esp32/esp-idf/components/hal/esp32c6/include/hal/i2c_ll.h:521
 (inlined by) i2c_isr_receive_handler at /home/ewheeler/src/esp32/esp-idf/components/esp_driver_i2c/i2c_master.c:570
0x408038fe: i2c_master_isr_handler_default at /home/ewheeler/src/esp32/esp-idf/components/esp_driver_i2c/i2c_master.c:631

TP      : 0x40811200  T0      : 0x0000001f  T1      : 0x2000103c  T2      : 0x00000002  
S0/FP   : 0x4081145c  S1      : 0x40811784  A0      : 0x4081145c  A1      : 0x0000000a  
A2      : 0x00000001  A3      : 0x000000c8  A4      : 0x00000001  A5      : 0x4600c011  
A6      : 0x00000004  A7      : 0x00000000  S2      : 0x40811784  S3      : 0x00000001  
S4      : 0x00000000  S5      : 0x00000000  S6      : 0x00000000  S7      : 0x00000000  
S8      : 0x00000000  S9      : 0x00000000  S10     : 0x00000000  S11     : 0x00000000  
T3      : 0x00000000  T4      : 0x00000000  T5      : 0x00000000  T6      : 0x00000000  
MSTATUS : 0x00001881  MTVEC   : 0x40800001  MCAUSE  : 0x00000018  MTVAL   : 0x00008391  
0x40800001: _vector_table at /home/ewheeler/src/esp32/esp-idf/components/riscv/vectors_intc.S:54

MHARTID : 0x00000000  


Backtrace:


0x40803702 in i2c_ll_is_bus_busy (hw=0x0) at /home/ewheeler/src/esp32/esp-idf/components/hal/esp32c6/include/hal/i2c_ll.h:521
521	    return hw->sr.bus_busy;
#0  0x40803702 in i2c_ll_is_bus_busy (hw=0x0) at /home/ewheeler/src/esp32/esp-idf/components/hal/esp32c6/include/hal/i2c_ll.h:521
#1  i2c_isr_receive_handler (i2c_master=i2c_master@entry=0x4081145c) at /home/ewheeler/src/esp32/esp-idf/components/esp_driver_i2c/i2c_master.c:570
#2  0x408038fe in i2c_master_isr_handler_default (arg=0x4081145c) at /home/ewheeler/src/esp32/esp-idf/components/esp_driver_i2c/i2c_master.c:631
#3  0x40800e76 in shared_intr_isr (arg=<optimized out>) at /home/ewheeler/src/esp32/esp-idf/components/esp_hw_support/intr_alloc.c:445
#4  0x4080a1b2 in _global_interrupt_handler (sp=<optimized out>, mcause=<optimized out>) at /home/ewheeler/src/esp32/esp-idf/components/riscv/interrupt.c:90
#5  0x4080026c in _interrupt_handler () at /home/ewheeler/src/esp32/esp-idf/components/riscv/vectors.S:352
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
ELF file SHA256: b48de9005

More Information.

This is caused because the i2c_mater driver busy waits in the ISR. Increasing CONFIG_ESP_INT_WDT_TIMEOUT_MS will delay the watchdog trigger, but of course that is not a fix.

esp-idf/components/esp_driver_i2c/i2c_master.c

Lines 566 to 569 in 5a40bb8

	IRAM_ATTR static void i2c_isr_receive_handler(i2c_master_bus_t *i2c_master)
	{
	i2c_hal_context_t *hal = &i2c_master->base->hal;
	while (i2c_ll_is_bus_busy(hal->dev)) {}

Suggestion:

Do not spin forever. Ideally this code would:

1. spin for only CONFIG_ESP_INT_WDT_TIMEOUT_MS / 2
2. exit the ISR
3. set i2c_master->status to ESP_ERR_INVALID_STATE, and
4. abort the transaction

I started to workup a patch for this, but I'm not sure how to check the ESP32 equivalent of a "time-step-counter" in an interrupt context.

Is there a way?

[mythbuster5]

Actually, For synchronous transaction, this line can be removed. For shout cut situation. Timeout interrupt can handle this properly. I will provide a quick fix.