GIET-VM / HBA Driver

The hba_driver.c​ and hba_driver.h​ files define the HBA driver.

The vci_multi_ahci component is a multi-channels, block oriented, external mass storage controller respecting the AHCI standard. Each channel define an independant physical disk, but this driver supports only one channel, because the GIET-VM uses only one physical disk.

The Command List is a software FIFO that can contain up to 32 independant commands, posted by different user tasks. These independant transfers are handled by the HBA device in the same order as they have been written in the command list. There is no global lock protecting the the HBA device, but the command list being a shared structure, the driver uses an atomic_increment() to get a slot in the command list, and increment the write pointer.

This driver implements two operating mode:

• In synchronous mode, the calling task uses a polling strategy on the HBA_PXCI register to detect the command completion (busy waiting). It does not use interrupt. This mode is used by the boot code to load the map.bin file into memory (before MMU activation), or to load the .elf files (after MMU activation).
• In descheduling mode, the calling task is descheduled, and the calling task global index is saved in the _hba_gtid[32] array, indexed by the command index. The task must be reactivated when the command is completed. This mode is used, to handle the user system calls.

As several user tasks can concurrently register commands in the command list, and there is only one HBA interrupt per channel, this interrupt is not linked to a specific calling task: in descheduling mode, the HBA IRQ is a "global" IRQ that is statically routed to processor P[x_io,y_io,0] in cluster_io. The associated global HBA_ISR send a WAKUP WTI to all tasks that have a completed command. This HBA_ISR uses a read pointer on the Command List to identify the expected command completion. The incrementation of this read pointer does not require atomic_increment as there is no concurrent access on this pointer.

The SEG_IOC_BASE address must be defined in the hard_config.h file.

The addressable registers map is defined here​.

Access Functions

unsigned int _hba_init ( )

This function checks the block size and desactivates interrupts. It initializes the HBA hardware registers, and the Command List. Return 0 for success, > 0 if error.

unsigned int _hba_access( unsigned int use_irq , unsigned int to_mem , unsigned int lba , unsigned long long paddr, unsigned int count )

This function register a command in the Command List (and associated Command Table) for a single physical buffer, and updates the HBA_PXCI register.

• use_irq: Boolean => request to use the descheduling mode if non zero
• to_mem : Boolean => to memory transfer if non zero
• lba : logic bloc address on device
• paddr : memory buffer physical base address
• count : number of blocs

Returns 0 if success, > 0 if error.

void _hba_isr( unsigned int irq_type , unsigned int irq_id , unsigned int channel )

This Interrupt Service routine is only used in the descheduling mode. It analyses the HBA_PXCI register, and for all completed commands, it saves the status value in the _hba_status[32] array, indexed by the command index, and activates the task waiting completion of this command.

• irq_type : HWI / PTI / WTI
• irq-id : index returned by XCU
• channel : unused (only one HBA channel is supported).