Interconnectivity
Page 21 of 22
Firmware Programming Guide for PDIUSBD12
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8.3 DMA Configuration Register
The D12's DMA operation is controlled by its DMA Configuration Register, which is set by the command Set
DMA. Not all the bits inside the register are related to the DMA operation. Bit 4 (Interrupt Pin Mode) together
with Bit 7 of Clock Division Factor (SOF-ONLY) controls D12 sources of interrupt.
The table below is a summary of the recommended register programming:
Bit
Name
DMA Mode
Non-DMA Mode
0 & 1
DMA Burst
‘1’ & ‘1’
Don’t care
2
DMA Enable
‘1’
‘0’
3
DMA Direction
‘1’ for IN token;
‘0’ for OUT token
Don’t care
4
Auto Reload
‘0’
Don’t care
5
Interrupt Pin Mode
‘0’
‘0’
6
Endpoint 4 Interrupt Enable
‘0’
‘1’
7
Endpoint 5 Interrupt Enable
‘0’
‘1’
By default, both D12 and DMAC are not in auto-reload mode. We do not want the device's DMA "auto-restart"
because this is a protocol-based operation, that is, under host's control. At EOT, both of D12 and DMA
controller's DMA will be disabled. The firmware needs to re-enable them to restart DMA transfer upon
receiving Setup DMA Request from the host.
Please also note that the interrupt from endpoints 4 and 5 are disabled in DMA mode. Servicing interrupt on
these endpoints is unnecessary and has a potential flaw during the DMA transfer. DMA can be treated as the
highest "interrupt" that happens between any CPU instructions, even inside ISR. Any routines that may want to
be used to check DMA status are not reliable because the DMA status during the transfer may change at any
time.
8.4 Setup DMA Request
Setup DMA request is a vendor request that is sent through control pipe. In PDIUSBD12 sample firmware and
Applet, this is done by IOCTL_WRITE_REGISTER, which is defined by Microsoft Still Image USB Interface
in Windows 98 DDK. The device's request is described below.
Offset
Field
Size
Value
Comments
0
BmRequestType
1
0x40
Vendor request, device to host
1
Brequest
1
0x0C
Fixed value for IOCTL_WRITE_REGISTER
2
Wvalue
2
0
Offset, set to zero
4
Windex
2
0x0471
Fixed value of Setup DMA Request
6
Wlength
2
6
Data length of Setup DMA Request
The details requested by the DMA operation are sent in the data phase after the device's request. The sample
firmware and Applet use a proprietary definition, which is shown below:
Offset
Field
Comments
0
Address [7:0]
The start address of requested DMA transfer.
1
Address [15:8]
2
Address [23:16]
3
Size [7:0]
The size of transfer.
4
Size [15:8]
5
Command
Bit 7: ‘1’ start DMA transfer
Bit 0: ‘1’ IN token; ‘0’ OUT token
