MEC1404 Datasheet, PDF (352/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
Data will be transfered between the DMA Master, starting at the programmed DEVICE_ADDRESS, and the targeted
memory location, starting at the MEMORY_START_ADDRESS. The address for either the DMA Master or the targeted
memory location may remain static or it may increment. To enable the DMA Master to increment its address set the
INCREMENT_DEVICE_ADDRESS bit. To enable the targeted memory location to increment its addresses set the
INCREMENT_MEMORY_ADDRESS. The DMA transfer will continue as long as the target memory address being
accessed is less than the MEMORY_END_ADDRESS. If the DMA Controller detects that the memory location it is
attempting to access on the Target is equal to the MEMORY_END_ADDRESS it will notify the DMA Master that the
transaction is done. Otherwise the Data will be transferred in packets. The size of the packet is determined by the
TRANSFER_SIZE.
24.9.2 OPERATION
The DMA Controller is designed to move data from one memory location to another.
24.9.2.1 Establishing a Connection
A DMA Master will initiate a DMA Transaction by requesting access to a channel. The DMA arbiter, which evaluates
each channel request using a basic round robin algorithm, will grant access to the DMA master. Once granted, the chan-
nel will hold the grant until it decides to release it, by notifying the DMA Controller that it is done.
Note: If Firmware wants to prevent any other channels from being granted while it is active it can set the
LOCK_CHANNEL bit.
24.9.2.2 Initiating a Transfer
Once a connection is established the DMA Master will issue a DMA request to start a DMA transfer.
Firmware can initiate a transaction by setting the TRANSFER_GO bit. The DMA transfer will remain active until either
the Master issues a Terminate or the DMA Controller signals that the transfer is DONE. Firmware may terminate a trans-
action by setting the TRANSFER_ABORT bit.
Note: Before initiating a DMA transaction via firmware the hardware flow control must be disabled via the DIS-
ABLE_HARDWARE_FLOW_CONTROL bit.
Data may be moved from the DMA Master to the targeted Memory address or from the targeted Memory Address to the
DMA Master. The direction of the transfer is determined by the TRANSFER_DIRECTION bit.
Once a transaction has been initiated firmware can use the STATUS_DONE bit to determine when the transaction is
completed. This status bit is routed to the interrupt interface. In the same register there are additional status bits that
indicate if the transaction completed successfully or with errors. This bits are OR’d together with the STATUS_DONE
bit to generate the interrupt event. Each status be may be individually enabled/disabled from generating this event.
24.9.2.3 CRC Generation
A CRC generator can be attached to a DMA channel in order to generate a CRC on the data as it is transfered from the
source to the destination. The CRC used is the CRC-32 algorithm used in IEEE 802.3 and many other protocols, using
the polynomial x³² + x²⁶ + x²³ + x²² + x¹⁶ + x¹² + x¹¹ + x¹⁰ + x⁸ + x⁷ + x⁵ + x⁴ + x² + x + 1. The CRC generation takes
place in parallel with the data transfer; enabling CRC will not increase the time to complete a DMA transaction. The CRC
generator has the optional ability to automatically transfer the generated CRC to the destination after the data transfer
has completed.
CRC generation is subject to a number of restrictions:
• The CRC is only generated on channels that have the CRC hardware. See Table 24-6, "DMA Channel N Register
Summary" for a definition of which channels have the ability to generate a CRC
• The DMA transfer must be 32-bits
• If CRC is enabled, DMA interrupts are inhibited until the CRC is completed, including the optional post-transfer
copy of it is enabled
• The CRC must be initialized by firmware. The value FFFFFFFFh must be written to the Data Register in order to
initialize the generator for the standard CRC-32-IEEE algorithm
24.9.3 DMA REGISTERS
The DMA Controller consists of a single Main Block of registers that applies to all channels and channel specific regis-
ters. Table 24-4, "DMA Main Register Summary" lists the registers in the Main Block and Table 24-6, "DMA Channel N
Register Summary" lists the registers in each channel.
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