Description
Basic Infos
- This issue complies with the issue POLICY doc.
- I have read the documentation at readthedocs and the issue is not addressed there.
- I have tested that the issue is present in current master branch (aka latest git).
- I have searched the issue tracker for a similar issue.
- If there is a stack dump, I have decoded it.
- I have filled out all fields below.
Platform
- Hardware: [ESP-12]
- Core Version: [latest git 10/19/2019]
- Development Env: [Arduino IDE]
- Operating System: [Windows]
Settings in IDE
- Module: [Wemos D1 mini r2]
- Flash Mode: [qio]
- Flash Size: [4MB]
- lwip Variant: [v2 Lower Memory]
- Reset Method: [ck]
- Flash Frequency: [40Mhz]
- CPU Frequency: [80Mhz]
- Upload Using: [SERIAL]
- Upload Speed: [921600] (serial upload only)
Problem Description
Doing Wire.status() from inside a sketch returns zero, but leaves SDA low, killing the bus.
Short example sketch, with D4 configured as OUTPUT_OPEN_DRAIN and optionally shorted to SDA to simulate a 'stuck slave' during testing. core_esp8266_si2c.cpp was modified to support the 'stuck slave' test, but the error occurs with or without any changes to core_esp8266_si2c.cpp
/* brief test to simulate a stuck slave using D4 OUTPUT_OPEN_DRAIN
shorted to SDA, do one write to show the bus is working, then force
D4 low and do Wire.status().
*/
#include <Wire.h>
void setup() {
Serial.begin(115200);
pinMode(D4, OUTPUT_OPEN_DRAIN);
}
void loop() {
GPOS = (1 << 2); // D4 connected to SDA to simulate a 'stuck slave', starts off not stuck
delayMicroseconds(5);
Wire.begin();
Wire.beginTransmission(0x76); // arbitrary address for test to show the bus works
Wire.endTransmission();
delayMicroseconds(5);
GPOC = (1 << 2); // simulate stuck slave, cleared inside Twi::status() bus recovery sequence
delayMicroseconds(5);
int err = Wire.status();
Serial.print("Wire.status return = ");
Serial.println(err);
err = digitalRead(SDA);
Serial.print("state of SDA = ");
Serial.println(err);
delay(100);
}Debug Messages (none)
Serial output shows:
Wire.status return = 0
state of SDA = 0
Clean return from Wire.status() as it kills SDA just before exit.
The proposed pull request adds a STOP after the START at the end of Twi::status(), releasing the bus. Added a bit of extra error-state checking by first checking for clock stretch before the initial SCL test, as the slaves and bus are in an unknown state when we first start Twi::status().
Additionally, there's an error in one of the clock stretch functions: you're comparing t (unsigned int) to twi_clockStretchLimit (uint32_t), surprising that it doesn't throw a warning.
Here are 2 logic analyzer captures of the fixed library, the first one a simple run ending with Wire.status(), the second with D4 shorted to SDA, causing a simulated 'stuck slave'.
The serial output with the fixed code shows:
Wire.status return = 0
state of SDA = 1
Here's the pull request:
https://github.com/Tech-TX/Arduino/pull/1
The small change I made to core_esp8266_si2c.cpp to test the 'stuck slave' is not included in the pull request. Inside the clock recovery loop in Twi::status() I set the D4 pin HIGH after several clocks so that it looked like a successfully recovered stuck slave.
int clockCount = 20;
while (SDA_READ() == 0 && clockCount-- > 0) { // if SDA low, read the bits slaves have to sent to a max
twi_read_bit();
if (SCL_READ() == 0) {
return I2C_SCL_HELD_LOW_AFTER_READ; // I2C bus error. SCL held low beyond slave clock stretch time
}
if (clockCount == 16) {
GPOS = (1 << 2); // release our 'stuck slave' test
}
}