Fix equipment readings 404 errors and implement BK Precision protocol support #100
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…rors
Equipment was failing with "InvalidSession: The resource might be closed" errors
when the VISA resource manager was recreated (e.g., during discovery or when
validating resource manager health). This happened because:
1. Resource manager recreation invalidates all instrument sessions opened by the old manager
2. Equipment instances retained references to invalid instrument handles
3. Any subsequent operations on those instruments would fail with InvalidSession
Solution:
- Added `_is_instrument_valid()` method to check if instrument session is still valid
- Added `_ensure_connected()` method to auto-reconnect when invalid session detected
- Updated `_write()`, `_query()`, and `_query_binary()` to validate and reconnect
- Added `_is_connecting` flag to prevent recursion during connection
Benefits:
- Equipment automatically recovers from invalid sessions
- No manual reconnection required when resource manager is recreated
- Transparent to API consumers - operations just work
- Proper logging when auto-reconnection occurs
This fixes the 500 Internal Server Error on /api/equipment/{id}/readings endpoint
that occurred after resource manager recreation.
The auto-reconnect logic was failing because when the resource manager was recreated (e.g., during discovery), equipment instances still held references to the old, invalid resource manager. When equipment tried to reconnect after detecting an invalid session, the reconnection would fail with the same InvalidSession error because self.resource_manager.open_resource() was called on a closed manager. Solution: - Added _is_resource_manager_valid() to check if resource manager is valid - Added _refresh_resource_manager() to create a new manager if invalid - Updated connect() to refresh resource manager before opening instruments This ensures that auto-reconnection can always succeed by creating a fresh resource manager when needed.
The BK power supply class overrides the base connect() method but wasn't calling _refresh_resource_manager() before opening the instrument. This caused auto-reconnection to fail when the resource manager became invalid. This fix ensures that the resource manager is validated and refreshed before attempting to open the instrument connection, preventing InvalidSession errors during auto-reconnection.
When reconnecting after an invalid session, the old instrument wasn't being closed before opening a new one. This caused the serial port's file descriptor to become None, leading to TypeError during reads. Changes: - Close old instrument in base.connect() before opening new resource - Close old instrument in BKPowerSupplyBase.connect() before opening - Close old instrument in _ensure_connected() before reconnecting This ensures proper cleanup of file descriptors and prevents conflicts when the same resource is opened multiple times.
…f SCPI
The BK Precision 1900B series (including 1902B) doesn't support SCPI commands.
They use a proprietary protocol with different command format and line endings.
Changes:
- Changed termination from '\r\n' (CR+LF) to '\r' (CR only)
- Replaced SCPI commands with BK Precision commands:
* *IDN? → GMAX (for verification)
* VOLT <value> → VOLT{vvv} (voltage * 10, 3 digits)
* CURR <value> → CURR{ccc} (current * 10, 3 digits)
* OUTP ON/OFF → SOUT0/SOUT1 (0=ON, 1=OFF)
* MEAS:VOLT?/MEAS:CURR? → GETD (returns VVVVIIIIIM format)
* VOLT?/CURR? → GETS (returns VVVCCC format)
* OUTP? → GOUT (returns 0=OFF or 1=ON)
Response parsing:
- GMAX/GETS format: VVVCCC (voltage÷10, current÷10)
- GETD format: VVVVIIIIIM (voltage÷100, current÷1000, mode 0/1)
- All responses end with \rOK\r which is stripped
This fixes timeout errors where the BK1902B wasn't responding to SCPI
commands because it doesn't understand that protocol.
When read_termination is set to '\r', PyVISA stops at the FIRST '\r'
and leaves the rest ('OK\r') in the buffer. This caused subsequent
reads to get 'OK' instead of actual data, resulting in empty responses.
Changes:
- Modified _bk_query to read full response byte-by-byte until 'OK\r'
- Added asyncio import for event loop timing
- No longer relies on read_termination for parsing BK responses
- Properly handles the complete response format: DATA\rOK\r
This fixes "Invalid GETD response:" errors where the response was
empty due to buffer contamination from previous reads.
X9X0
deleted the
claude/fix-equipment-readings-404-011YNFgs3A54537srRvDcAe6
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Summary
Fixes equipment readings returning 404 Not Found errors and implements proper protocol support for BK Precision 1900B series power supplies.
Problems Fixed
1. Equipment 404 Errors
404 Not Founderrors when trying to access equipment readings after reconnection2. Invalid VISA Session Errors
3. BK Precision Communication Failures
4. Serial Port Resource Leaks
NoneTypeerrors5. Response Buffer Contamination
\r, leavingOK\rin bufferChanges Made
Deterministic Equipment IDs
ASRL/dev/ttyUSB0::INSTR→ps_56fdd3df)Auto-Reconnection System
_is_instrument_valid()to detect invalid VISA sessions_ensure_connected()to auto-reconnect on invalid sessions_is_resource_manager_valid()to detect invalid resource managers_refresh_resource_manager()to create new resource manager when needed_write(),_query(), and_query_binary()operationsBK Precision Protocol Support
\r\nto\ronlyGMAX- Get max voltage/current (format: VVVCCC)GETS- Get voltage/current settings (format: VVVCCC)GETD- Get display readings (format: VVVVIIIIIM)GOUT- Get output state (0=OFF, 1=ON)VOLT{vvv}- Set voltage (voltage × 10)CURR{ccc}- Set current (current × 10)SOUT0/SOUT1- Set output (0=ON, 1=OFF)\rOK\rwhich is properly parsedProper Resource Cleanup
Response Buffer Handling
OK\rterminatorTesting
Tested with BK Precision 1902B power supply:
Commits
2140b60- Generate deterministic equipment IDs to prevent 404 errors27a6e9a- Add automatic VISA session recovery to prevent InvalidSession errorsea3b8a5- Refresh resource manager during auto-reconnectiond6a9191- Call _refresh_resource_manager() in BK power supply connect method09da3e5- Properly close old instrument before reconnection3bf6cf7- Update BK Precision driver to use proprietary protocol instead of SCPI408a45c- Read full BK Precision response including OK terminatorBreaking Changes
None - all changes are backward compatible improvements to existing functionality.