Open source FreeRTOS SDK for EOS S3 MCU+eFPGA SoC including gateware, software and documentation under QuickLogic Open Reconfigurable Computing (QORC) Initiative
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fix uart hal for spurious rx with floating rx pin #142
qf_apps/qf_bootloader_uart : if UART cable is not connected from HOST to the EOSS3 (specifically the Rx pin of the EOSS3): the board keeps resetting after pressing the 'USR' button, and never stays in the 'programming' mode.
Cause:
EOSS3 gets Rx interrupts due to the UART Rx pin floating - the 'data' in the register is always '0' and the 'framing_error' bit is always set. This happens continuously and does not die down.
As the 'data' part of this is pushed into the Rx Buffer, the bootloader loop gets a '0' which is considered to be the 'boot' command in normal scenarios, causing the reset of the board.
Fix:
2 parts:
For Rx Interrupts where the 'framing_error' is set, do not consider the 'data' part of the register as valid bytes, so add a 'return'
Also, when the 'framing_error' count reaches a threshold, disable the UART interrupts, otherwise the interrupt handler hogs the CPU indefinitely. A nominal threshold of '5' errors is currently used, as the ideal scenario is '0' errors.
Test
Current:
Keep the UART cable unconnected to the QuickFeather, and then run the qf_bootloader_uart, and press 'USR' button to enter 'programming' mode: board continuously resets
Keep the UART cable connected, and then run the qf_bootloader_uart and press 'USR' button to enter 'programming' mode: board works as expected (stays in 'programming' mode)
With Fix:
With either UART cable unconnected, or connected, with the qf_bootloader_uart, and press 'USR' button to enter 'programming' mode: the board works as expected (stays in 'progamming' mode)
Symptom:
qf_apps/qf_bootloader_uart: if UART cable is not connected from HOST to the EOSS3 (specifically the Rx pin of the EOSS3): the board keeps resetting after pressing the 'USR' button, and never stays in the 'programming' mode.Cause:
EOSS3 gets Rx interrupts due to the UART Rx pin floating - the 'data' in the register is always '0' and the 'framing_error' bit is always set. This happens continuously and does not die down. As the 'data' part of this is pushed into the Rx Buffer, the bootloader loop gets a '0' which is considered to be the 'boot' command in normal scenarios, causing the reset of the board.
Fix:
2 parts:
Test
Current:
With Fix:
With either UART cable unconnected, or connected, with the qf_bootloader_uart, and press 'USR' button to enter 'programming' mode: the board works as expected (stays in 'progamming' mode)