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iic_transfer
Hardware Abstraction Layer
» List of HAL APIs
» HAL IIC API
» iic_transfer structure
"C" style construct
typedef struct iic_transfer
{
unsigned addr:8;
unsigned :21;
unsigned riscos_retry:1;
unsigned checksumonly:1;
unsigned nostart:1;
union
{ unsigned checksum;
void *data;
} d;
unsigned len;
} iic_transfer;
Assembler method
R0 points to the data block which is a list of transfers set out as:-
Word 0
bit 0 = Write/Read
bit 1-7 = Address of device
bit 8-28 = Reserved
bit 29 = Retry flag
bit 30 = Return checksum only flag
bit 31 = Send no start flag
Word 1 = Pointer to memory for data to be sent/received
Word 2 = Length of data to send/receive
This is repeated for the number of transfers required (R1)
Use
This structure is used to describe a transfer as performed by the high-level HAL IIC API. It is also used by RISCOS_IICOpV and the OS_IICOp SWI.
- A full IIC transfer (from START bit to STOP bit) is described by one or more iic_transfer structures, arranged in a list
- Each subtransfer is described by a single iic_transfer
- The direction of the subtransfer is determined by the least significant bit of addr, as per the IIC spec (1=Read, 0=Write).
- If nostart is 0, a START is first transmitted followed by addr, otherwise the data flow continues where the previous subtransfer left off. nostart must be 0 for the first subtransfer.
- For writes, len bytes of data are read from data and transmitted across the bus.
- For reads, len bytes of data are read from the bus and:
- Written to data if checksumonly = 0
- Summed to checksum if checksumonly = 1, to produce a 32bit checksum
- The riscos_retry bit is of no concern to HAL IIC drivers. Retries are the sole responsibility of RISC OS; if riscos_retry is set for the first transfer of a list sent via RISCOS_IICOpV/OS_IICOp, then RISC OS will retry the transfer list if it fails due to bus-busy or no-ack errors.
- Other bits are reserved and should be zero.