| # Using I2C host for SMBus commands |
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| The I2C host can generate all the SMBus commands listed in the Rev 3.0 SMBus specification. |
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| ### Quick Command |
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| The Quick command is a rare case where the Start and Stop properties are both set on the same write to the I2C FIFO, along with an address and single bit of data. |
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| ### Simple commands |
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| The simple SMBus commands are essentially single byte I2C transactions. |
| A Start is attached to an address with either the write or read flag. |
| There follows a single byte transfer in the appropriate direction with the Stop flag attached. |
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| ### Writes |
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| The set of SMBus Writes (Byte, Word, 32-bit and 64-bit) follow the address with a command byte and then the appropriate number of data bytes. |
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| Host Notify is the same as Write Word but uses special addresses (and would come from a device). |
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| ### Reads |
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| The SMBus read commands start by writing a command byte then have a repeated start before the data transfer. |
| Note that read entry in the I2C fifo includes the data length, so only one entry is needed for all the cases, and it will always include the Stop. |
| The data received from the device is read from the RDATA FIFO. |
| The interface will automatically NACK the last byte in the transfer. |
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| ### Process Call |
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| The SMBus Process Call consists of a command and two bytes transferred in each direction. |
| As with the Reads there is a repeated start before the transfer from the device. |
| Note that in the write direction each byte is written to the fifo, and for the read direction just the single entry with the 2 byte transfer size. |
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| ### Block Write |
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| A Block Write is a potentially longer write that includes the command and an explicit length byte (N) before N bytes of data. |
| Since this may transfer up to 255 bytes the driver code is likely to need to manage the I2C fifo becoming full. |
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| ### Block Read |
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| A Block Read is a potentially longer read where the length of data being transferred is reported by the device during the transaction. |
| This requires the transaction to be split into two stages. |
| The first part of the transaction is similar to a Byte Read, except instead of the Stop flag the RCont flag is set on the one-byte read. |
| The RCont flag causes the interface to read the byte and generate an ACK to keep the transaction alive. |
| Since the I2C fifo will be empty at this point the interface will extend the clock low time. |
| The driver then needs to read the value (N) from the RDATA fifo to know the size of the rest of the transaction and write the I2C fifo with N and the Read and Stop flags set. |
| The transaction now completes with N bytes read from the device. |
| If the RDATA fifo fills then the clock will again be stretched until there is space for more data. |
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| ### Block Write Read Process Call |
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| The most complex transaction combines a block write and a block read. |
| (Note that there may be a different number of bytes transferred in each direction despite the same N being shown in the diagrams below and SMBus specification.) |
| This has the same split character as Block Read. |
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