= GIET_VM / MWR Driver =

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The [source:soft/giet_vm/giet_drivers/mwr_driver.c mwr_driver.c] and [source:soft/giet_vm/giet_drivers/mwr_driver.h mwr_driver.h] files define the MWR driver for the vci_mwmr_dma peripheral.

The vci_mwmr_dma component is a multi-channels DMA controller that can be used to connect an hardware coprocesseur to a VCI interconnect.
This component provides the coprocessor one or several TO_COPROC or FROM_COPROC FIFO type communication channels, without address.
Each T0_COPROC/FROM_COPROC port contains an hardware FIFO interface (DATA, R_WOK, W_ROK signals), plus three signals (REQ, ACK, BURSTS) allowing the coprocessor
to request an integer number of data burst. Each burst contains a fixed number of 32 bits words. The burst length is an hardware parameter.

Each channel implements two running modes:
 * in '''MWMR''' mode the channel FSM transfer an infinite" stream of data to or from a MWMR software FIFO, implementing the 7 steps MWMR protocol.
 * in '''DMA''' mode the channel FSM transfer a fixed size chunk of data to or from a memory buffer, with an optional completion signaling interrupt.

It is an ''internal'' peripheral, that can be replicated in all clusters. 

The addressable registers map and command codes are defined [source:soft/giet_vm/giet_drivers/mwr_driver.h here].

 === void '''_mwr_channel_init'''( unsigned int cluster_xy, unsigned int channel, unsigned int mode, unsigned long long buffer_paddr, unsigned int buffer_size, unsigned long long desc_paddr, unsigned long long lock_paddr ) ===
This function initialises all registers defining one communication channel for a given coprocessor.
 * '''cluster_xy''' is the cluster index
 * '''channel''' is the channel index
 * '''mode''' is the requested mode (MWMR / DMA_IRQ / DMA_NO_IRQ)
 * '''buffer_paddr''' is the memory buffer physical address
 * '''buffer_size''' is the memory buffer size (bytes)
 * '''desc_paddr''' is the MWMR descriptor physical address (only used in MWMR mode)
 * '''lock_paddr''' is the MWMR lock physical address (only used in MWMR mode)

 === void '''_mwr_channel_start'''( unsigned int cluster_xy,  unsigned int channel ) ===
This function activates one communication channel for a given coprocessor (set a non zero value in the RUNNING channel register).
 * '''cluster_xy''' is the cluster index
 * '''channel''' is the channel index

 === void '''_mwr_channel_stop'''( unsigned int cluster_xy,  unsigned int channel ) ===
This function desactivates one communication channel for a given coprocessor (set a zero value in the RUNNING channel register).
 * '''cluster_xy''' is the cluster index
 * '''channel''' is the channel index

 === void '''_mwr_isr( unsigned int irq_type,  unsigned int irq_id,  unsigned int channel )
This Interrupt Service Routine handles the IRQ signaling the completion of a data transfer for a channel running in DMA_IRQ mode).
It set the _dma_done[x][y] synchronisation variable.