diff options
Diffstat (limited to 'NOTES')
| -rw-r--r-- | NOTES | 42 |
1 files changed, 35 insertions, 7 deletions
@@ -157,19 +157,47 @@ exact read: read exactly specified number of bytes (should be error should be returned) ignore packets: autoterminate each buffer, depends on engine configuration -autogrow: automatic memory allocation, only through streaming + + To handle differnt cases, the value returned by callback function instructs +the DMA library how long to wait for the next data to appear before timing +out. The following variants are possible: +terminate: just bail out +check: no timeout, just check if there is data, otherwise + terminate +timeout: standard DMA timeout, normaly used while receiving + fragments of packet: in this case it is expected + that device has already prepared data and only + the performance of DMA engine limits transfer speed +wait: wait until the data is prepared by the device, this + timeout is specified as argument to the dma_stream + function (standard DMA timeout is used by default) first | new_pkt | bufer -------------------------- -standard wait | term | wait -multiple packets wait | check | wait - DMA_READ_FLAG_MULTIPACKET -waiting multipacket wait | wait | wait - DMA_READ_FLAG_WAIT -exact wait | wait/term | wait - limited by size parameter -ignore packets wait | check | check - just autoterminated -autogrow +standard wait | term | timeout +multiple packets wait | check | timeout - DMA_READ_FLAG_MULTIPACKET +waiting multipacket wait | wait | timeout - DMA_READ_FLAG_WAIT +exact wait | wait/term | timeout - limited by size parameter +ignore packets wait | wait/check| wait/check - just autoterminated 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. + + - Actually, we can make another in-module buffering. But this hopefully can + be avoided. + + Register Access Synchronization =============================== We need to serialize access to the registers by the different running |