| ??? 12/30/06 12:51 Modified: 12/30/06 12:59 Read: times |
#130243 - answer is partially incorrect Responding to: ???'s previous message |
Russel,
I don't want to score your message as incorrect because it has many good points, but the last one about atomicity is incorrect.
mov a, TX_BUF_HEAD ;TX_BUF_HEAD is not changed in the ISR
xrl a, TX_BUF_TAIL ;this is an atomic read
JZ TX_BUF_EMPTY_TEST
TX_BUF_NOT_EMPTY:
mov R0, TX_BUF_HEAD
mov @R0, TX_DB
inc TX_BUF_HEAD ;this is an atomic increment
anl TX_BUF_HEAD,#31 ;loop around
Only TX_BUF_TAIL is changed in the ISR and thus needs atomic read access in the main thread. Since it is only 1 byte the read is atomic by design. TX_BUF_HEAD is read in the ISR so updates in the main thread need to be atomic. Since it is also only 1 byte and incremented using inc this is fulfulled too. It will also need an overflow check for buffers <> 256 to make it a ring buffer. If the ISR does this too after the read there is no problem. Maarten |
| Topic | Author | Date |
| the nature of the UART/steping through interrupts | 01/01/70 00:00 | |
| Uart is full duplex | 01/01/70 00:00 | |
| Thanks Russell | 01/01/70 00:00 | |
| UART Question Part 2 | 01/01/70 00:00 | |
| You can not do both | 01/01/70 00:00 | |
| In response to Neil | 01/01/70 00:00 | |
| go with the bit | 01/01/70 00:00 | |
| In response to Neil | 01/01/70 00:00 | |
| In response to Neil | 01/01/70 00:00 | |
| Sorry for teh tripple post... | 01/01/70 00:00 | |
| More... | 01/01/70 00:00 | |
| Search and Read | 01/01/70 00:00 | |
| Thanks Russell | 01/01/70 00:00 | |
| I hope Russell did not lead you down the garden pa | 01/01/70 00:00 | |
| Erik - garden path indeed! | 01/01/70 00:00 | |
| I'm using interrupts | 01/01/70 00:00 | |
| Question about my interrupt driven UART | 01/01/70 00:00 | |
| You know the answer. | 01/01/70 00:00 | |
| Thanks Russell | 01/01/70 00:00 | |
answer is partially incorrect | 01/01/70 00:00 | |
| Can't single step on UART | 01/01/70 00:00 |