Content originally posted in LPCWare by npiergi on Fri Apr 11 13:46:09 MST 2014
Hi all.
I used the DAC to generate voice messages with 8-bit per samples at 8KHz rate. The samples are stored in RAM as 32 bits. I used DMA transfer from memory to the DAC. Everything works perfectly.
But using 32bit for 8-bit samples is too much! So I tried to store in RAM only 16bit (BIAS bit is excluded) per sample and to program the DMA with 16-bit size as source and 32-bit size as destination. It does not work. This is the piece of code used:
DMACC0CONTROL = 0xFFF // transfer size (0 - 11) = 4096
| (0 << 12) // source burst size (12 - 14) = 1
| (0 << 15) // destination burst size (15 - 17) = 1
| (1 << 18) // source width (18 - 20) = 2=32 bit 1=16bit
| (2 << 21) // destination width (21 - 23) = 32 bit
| (0 << 24) // source AHB select (24) = AHB 0
| (0 << 25) // destination AHB select (25) = AHB 0
| (1 << 26) // source increment (26) = increment
| (0 << 27) // destination increment (27) = no increment
| (0 << 28) // mode select (28) = access in user mode
| (0 << 29) // (29) = access not bufferable
| (0 << 30) // (30) = access not cacheable
| (0 << 31); // terminal count interrupt disabled
DMACC0CONFIGURATION = 1
| (0 << 1) // source peripheral (1 - 5) = none
| (7 << 6) // destination peripheral (6 - 10) = DAC
| (1 << 11) // flow control (11 - 13) = mem to per
| (0 << 14) // (14) = mask out error interrupt
| (0 << 15) // (15) = mask out terminal count interrupt
| (0 << 16) // (16) = no locked transfers
| (0 << 18); // (27) = no HALT
/* DACclk = 25 MHz, so 125 usec interval-> 25 * 125 = */
DACCNTVAL = 3125;
/* DMA, timer running, dbuff */
DACCTRL = 1<<3 | 1<<2 | 1<<1;
Where is the error? It's a mission impossible?
Thank in advance
