The Cortex-M0+ is an ultra low power 32-bit ARM processor designed for embedded and IoT applications. During development, users may encounter an error when trying to program or “flash” new firmware onto the chip, commonly referred to as the “Flash Download failed” error.
There are several potential causes for this error, which we will explore in detail below. The good news is that in most cases, this error can be resolved through proper configuration, interface and hardware setup, or software fixes. With some troubleshooting and tweaking, you should be able to successfully flash your Cortex-M0+ chip.
Common Causes of Flash Download Failed
Here are some of the most common reasons you may see the Flash Download failed error when working with a Cortex-M0+ processor:
Incorrect Debug Interface Configuration
The Cortex-M0+ chip needs to be put into debug mode in order to flash it. This requires proper configuration of the debug interface – usually SWD (Serial Wire Debug) or JTAG (Joint Test Action Group). Double check that the debug interface mode, speed, voltages, and connections match between the chip and debugger/programmer hardware.
Faulty Debugger/Programmer Hardware
The debugger or programmer hardware used to flash the Cortex-M0+ could itself be malfunctioning. Try substituting the hardware with a known good debugger/programmer if possible. Hardware issues like loose cabling, underpowered supply, or compatibility problems can also cause flashing to fail.
Invalid Flash Algorithm
The flash algorithm contains the low-level code for erasing and reprogramming the Cortex-M0+ flash memory. An incorrect flash algorithm that does not match the target chip will lead to flash download failures. Verify the algorithm is for the exact flash on your chip.
Insufficient Power or Decoupling
Flashing the Cortex-M0+ flash requires a stable power supply to the chip, along with proper decoupling capacitors close to the chip’s power pins. Insufficient power or decoupling can cause brownouts or glitches during flash programming, resulting in failures.
Code Size Too Large
If the code size being flashed exceeds the total flash storage size of the Cortex-M0+ chip, you will get download failed errors. Carefully check that the compiled firmware fits within the available flash size specified in the chip’s datasheet.
Invalid Flash Address Range
The starting address and size of the flash range being programmed must align with the valid address ranges exposed by the Cortex-M0+ flash memory. Trying to program outside the spec’d ranges will fail. Double check addresses match the datasheet.
Flash Protection Enabled
Some Cortex-M0+ chips have flash protection or read-only modes that can be enabled. This prevents any attempted write to flash, causing the flash downloader to fail. The protection must be disabled via a debugger/programmer before re-flashing the chip.
Flash ECC Errors
Error correction code (ECC) in the Cortex-M0+ flash can detect and correct a limited number of flash bit errors. Too many errors can result in uncorrectable errors during flash programming that lead to failure. This may indicate a poor quality or damaged flash chip.
Solutions for “Flash Download Failed”
Now that we’ve explored some potential reasons for seeing the notorious “Flash Download Failed” error, here are some steps you can take to resolve it when flashing your Cortex-M0+ processor:
1. Verify Interface Configuration
Double and triple check that the SWD or JTAG interface settings match between the debugger/programmer and the target chip. This includes voltage levels, clock speeds, connector pins, and protocols.
2. Substitute Debug Hardware
Try swapping out the debugger/programmer hardware with proven models to isolate any hardware issues. Loose cables, underpowered adapters, and compatibility problems can appear as flash download failures.
3. Check Flash Algorithm
Confirm the flash algorithm matches the specific flash memory model in your chip and follows the programming steps outlined in the datasheet. Using an incorrect algorithm is a common cause of flash failures.
4. Increase Power/Decoupling
Ensure adequate power and clean stable voltages are supplied to the Cortex-M0+ during flashing. Add decoupling capacitors close to supply pins if needed to reduce noise/ripple.
5. Verify Code Size
Check that the compiled firmware size does not exceed the Cortex-M0+ flash capacity specified in the datasheet. Oversize code is guaranteed to fail flashing.
6. Correct Flash Addresses
Confirm the flash start address and length programmed fall within the address ranges exposed by the flash. Out of range writes will be rejected.
7. Unlock Flash Protection
Disable any write protection or read-only modes on the flash using a debugger/programmer before attempting to reprogram it. Protected flash cannot be erased/written.
8. Reflash Chip
As a last resort, completely erase and reflash the Cortex-M0+ chip from scratch after correcting any issues. This can eliminate persistent flash errors.
Preventing Flash Download Failures
Once you have resolved any flash download issues, here are some tips to avoid Cortex-M0+ flash problems in the future:
- Always double check debug interface configurations match the target chip.
- Perform chip erase before flashing new firmware.
- Verify flash algorithm is correct for the exact flash part.
- Leave sufficient margin for code size within total flash size.
- Use proven, compatible debugger/programmer hardware.
- Check voltages and increase decoupling capacitance.
- Watch for flash ECC errors indicating possible bad flash.
With good programming hygiene, the dreaded “Flash Download Failed” error can be banished for good from your Cortex-M0+ projects.
Conclusion
While flash download errors can certainly be frustrating, identifying the root cause is usually possible with some detailed troubleshooting. Configuration problems, hardware issues, software bugs, size mismatches and flash protections are all common culprits. Now armed with an understanding of the potential causes and solutions, you can swiftly resolve those Cortex-M0+ flash failures and get back to developing your embedded applications.
