what's the CMDWORDS means in iMX28 HW_APBH_CHn_CMD register ,and how to calculate it?

[liuxing]

what's the CMDWORDS means in iMX28 HW_APBH_CHn_CMD register ,and how to calculate it?

[Yuri]

  According to the Reference Manual (RM), CMDWORDS indicates the number

of command words to send to one of peripheral controllers, shown on Figure 6-1

(AHB-to-APBH Bridge DMA Block Diagram) of the RM – say, the SSP1 – in order

to initialize a needed operation.

  Usually any operation, where DMA is involved assumes two phases :

1) controller register initialization and operation (read / write) start ;
2) transfer data via DMA, assuming DMA is already configured. 
 

  The CMDWORS is intended for the first stage.

Have a great day,
Yuri

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[liuxing]

Hi,Yuri,

    Thanks a lot.

     I still don't know how to calculate the value of CMDWORS.

     for example, at chapter 16.4.1.1  of RM(page 1375),

     DMA Structure Code Example,

//----------------------------------------------------------------------------

// Descriptor 1: issue NAND write setup command (CLE/ALE)

//----------------------------------------------------------------------------

write[0].dma_nxtcmdar = &write[1]; // point to the next descriptor

write[0].dma_cmd = BF_APBH_CHn_CMD_XFER_COUNT (1 + 5)| // 1 byte command, 5 byte address

BF_APBH_CHn_CMD_CMDWORDS (3) | // send 3 words to the GPMI

BF_APBH_CHn_CMD_WAIT4ENDCMD (1) | // wait for command to finish

//----------------------------------------------------------------------------

// Descriptor 2: write the data payload (DATA)

//----------------------------------------------------------------------------

write[1].dma_nxtcmdar = &write[2]; // point to the next descriptor

write[1].dma_cmd = BF_APBH_CHn_CMD_XFER_COUNT (0)| // NOTE: No DMA data transfer

BF_APBH_CHn_CMD_CMDWORDS (4)| // send 4 words to the GPMI

BF_APBH_CHn_CMD_WAIT4ENDCMD (1)| // Wait to end

BF_APBH_CHn_CMD_SEMAPHORE (0)|

BF_APBH_CHn_CMD_NANDWAIT4READY (0)|

BF_APBH_CHn_CMD_NANDLOCK (1)| // maintain resource lock

BF_APBH_CHn_CMD_IRQONCMPLT (0)|

BF_APBH_CHn_CMD_CHAIN (1)| // follow chain to next command

BV_FLD(APBH_CHn_CMD, COMMAND, DMA_NO_XFER); // No data transferred

Why the CMDWORDS value of  Descriptor 1 is 3,and  its value of  Descriptor 2 is 4?How to calculate it?The CMDWORDS value will be different if the ECC enable or disable.why?