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Diffstat (limited to 'NOTES')
| -rw-r--r-- | NOTES | 34 |
1 files changed, 25 insertions, 9 deletions
@@ -186,16 +186,32 @@ Shall we do a special handling in case of overflow? Buffering ========= The DMA addresses are limited to 32 bits (~4GB for everything). This means we - can't really use DMA pages are sole buffers. Therefore, - 1. In streaming mode a second thread will be spawned copying the data from the - DMA pages into the allocated buffers. On duration expiration this thread - will be stopped but processing will continue until all copyied data is - passed to the callbacks. - 2. In synchronous mode, a single event will be extracted from the the DMA - memory. + can't really use DMA pages are sole buffers. Therefore, a second thread, with + a realtime scheduling policy if possible, will be spawned and will copy the + data from the DMA pages into the allocated buffers. On expiration of duration + or number of events set by autostop call, this thread will be stopped but + processing in streaming mode will continue until all copyied data is passed + to the callbacks. - - Actually, we can make another in-module buffering. But this hopefully can - be avoided. + To avoid stalls, the IPECamera requires data to be read continuously read out. + For this reason, there is no locks in the readout thread. It will simplify + overwrite the old frames if data is not copied out timely. To handle this case + after getting the data and processing it, the calling application should use + return_data function and check return code. This function may return error + indicating that the data was overwritten meanwhile. Hence, the data is + corrupted and shoud be droped by the application. The copy_data function + performs this check and user application can be sure it get coherent data + in this case. + + There is a way to avoid this problem. For raw data, the rawdata callback + can be requested. This callback blocks execution of readout thread and + data may be treated safely by calling application. However, this may + cause problems to electronics. Therefore, only memcpy should be performed + on the data normally. + + The reconstructed data, however, may be safely accessed. As described above, + the raw data will be continuously overwritten by the reader thread. However, + reconstructed data, upon the get_data call, will be protected by the mutex. Register Access Synchronization |