STM32: make i2c_salve_read return the number of bytes read

[pennam]

Summary of changes

If no timeout happens during communication i2c_slave_read(i2c_t *obj, char *data, int length) returned value is always equal to length parameter even if the master sends a lower number of bytes. Subsequently mbed-os read API will return always success.

The proposed solution is the same implemented here https://github.com/stm32duino/Arduino_Core_STM32/blob/655587065fbdd6324655fee0b13d268507e23a40/libraries/Wire/src/utility/twi.c#L1014

With this changes if the master writes 5 bytes and we read less than 5 bytes slave.read() will return success, same happens if we read exactly 5 bytes, but if we want to read 5 bytes and master writes only 4, slave.read() will return an error

Impact of changes

All ST targets

Migration actions required

Documentation

---

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

I've tested the changes on PORTENTA target using this code and works as described above.

#include "mbed.h"

// Blinking rate in milliseconds
#define BLINKING_RATE     500ms
#define BYTES_TO_READ     6

Thread thread;
I2CSlave slave(PH_8,PH_7);
I2C      master(PB_7,PB_6);

void slaveThread()
{
    char buf[10] = {0};

    slave.address(0xA0);
    while (1) {
        int i = slave.receive();
        switch (i) {
            case I2CSlave::ReadAddressed:
                break;
            case I2CSlave::WriteGeneral:
                break;
            case I2CSlave::WriteAddressed:
                int ret = slave.read(buf, BYTES_TO_READ);
                if(ret == 0) {
                    printf("Read A:");
                    for(int i = 0; i < BYTES_TO_READ; i++) {
                        printf(" %d",buf[i]);
                    }
                    printf("\n");
                } else {
                    printf("Read A: Error\n");
                }
                break;
        }
        for (int i = 0; i < 10; i++) {
            buf[i] = 0;    // Clear buffer
        }
    }
}

int main()
{
    // Initialise the digital pin LED1 as an output
    DigitalOut led(LED1);

    printf("Start slave thread\n");
    thread.start(slaveThread);

    while (1) {
        led = !led;

        printf("Master write\n");

        char cmd[5] = {0,1,2,3,4};
        master.write(0xA0, cmd, 5);

        ThisThread::sleep_for(BLINKING_RATE);
    }
}

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

@facchinm @jeromecoutant @0xc0170

---

[ciarmcom]

@pennam, thank you for your changes.
@0xc0170 @jeromecoutant @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

Please add info from description to the commit message (what is being fixed and why)

Also keep the style consistent in i2c_api.c file (if ( - space)

Pull request has been modified.

[mergify]

This PR cannot be merged due to conflicts. Please rebase to resolve them.

Pull request has been modified.

[pennam]

rebased to resolve conflict in targets/TARGET_STM/i2c_api.c

[0xc0170]

CI started

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jenkins-ci/mbed-os-ci_build-cloud-example-ARM	❌
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[pennam]

Need to update objects.h file of all ST platforms to PASS ci. @jeromecoutant what's your opinion on this changes? If you are OK with them i will fix the other targets. Thanks

[jeromecoutant]

Approved !

Pull request has been modified.

[pennam]

CI should be fixed now

[adbridge]

@0xc0170 looks like you added the label but didn't actually start the CI ?

[0xc0170]

@0xc0170 looks like you added the label but didn't actually start the CI ?

Correct, I had to wait until 5.15 job completed (the breakage in 5.15 to be cleared). Starting all master jobs now

[0xc0170]

CI started

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jenkins-ci/mbed-os-ci_unittests	✔️
jenkins-ci/mbed-os-ci_cmake-cloud-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_cmake-cloud-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-cloud-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_cmake-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_build-example-ARM	✔️
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