HAL: specify what flow control is

[pan-]

Description

• Enhancement
• Priority: Major

Enhancement

The function serial_set_flow_control enable hardware flow control of the serial port but there is no description of what flow control is.

The lack of specification is detrimental for coherence of the platform because the HAL maintainer is free to interpret what flow control is/should be.

Incoherence between ports is already in the code base, for instance, on the NRF52 based targets, the line CTS/RTS are active low while on the MAXIM32630 target those lines are active high.

Suggested enhancement

• Define polarity of control flow line; maybe a function to configure it can also be added.
• Detail what rxflow and txflow are and how they are supposed to work.
• Add (hardware) tests verifying the compliance of a port with the specification

[jessexm]

I agree a more detailed specification will help developers avoid differences in HAL implementations. This can also be used to determine if a particular peripheral can provide the functionality required by an API.

[Mirrored to Jira]

[maclobdell]

@pan- Just to confirm - no action is required now until the behavior of flow control signals is standardized by the hal specification, correct? So, right now the behavior may vary across platforms until we come to a consensus on a default behavior.
[Mirrored to Jira]

[adbridge]

Internal Jira reference: https://jira.arm.com/browse/IOTHAL-78

[ciarmcom]

Thank you for raising this issue. Please note we have updated our policies and
now only defects should be raised directly in GitHub. Going forward questions and
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issue is still relevant please re-raise it there.
This GitHub issue will now be closed.