QNX RTOS v4 Knowledge Base
QNX RTOS v4 Knowledge Base
| Title |
Direct Memory Access (DMA) Programming |
| Ref. No. |
QNX.000009412 |
| Category(ies) |
Development |
| Issue |
We are using QNX4 and Watcom 10.6, and we need to access a specific memory location for a video card utility that we are developing. We have no problems with port access functions using -T1 but the function requires us to write to a memory mapped IO location.
Any suggestions?
|
| Solution |
First, you should read through /etc/readme/technotes/shmem.txt.
This contains a useful overview and some examples of using the shared memory routines that will be used to map in card memory.
The basic sequence is:
--
int fd;
volatile char *ptr;
fd=shm_open("/dev/shmem/Physical",O_RDWR,0);
ptr = mmap(0,size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, linear_address);
--
Then, you can just treat ptr like a normal pointer to allocated memory, except that it may be changed asynchronously. |
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