Visible to Intel only — GUID: fkr1535469995032
Ixiasoft
Visible to Intel only — GUID: fkr1535469995032
Ixiasoft
8.4.1. FIFO Implementation
All FIFOs are used in peripheral channel to buffer up the incoming transactions. When the eSPI-to-LPC bridge is busy transferring data down the LPC interface, the transactions from the eSPI host are stored using the PC_RXFIFO or NP_RXFIFO until the bridge is idle. The PC_RXFIFO stores posted transactions while the NP_RXFIFO stores non-posted transactions.
The RXFIFOs can store more than one eSPI transaction (command byte, header byte and write data byte) until it is full. When the FIFO depth is less than MAX_PC_PAYLOAD_SIZE + 1 complete header + 1 command byte or 1 complete header + 1 command byte for NP_RXFIFO , the PC_FREE/NP_FREE status register bit is de-asserted.
The Pre_RXFIFO stores an incoming eSPI transaction for CRC error checking purposes. CRC error check is performed after pushing the last byte of a eSPI transaction into Pre_RXFIFO. If CRC error is high, then the eSPI transaction is dropped to avoid translation into a LPC transaction. If CRC error is low, the eSPI transaction is pushed into NP_RXFIFO or PC_RXFIFO for translating into a LPC transaction.
The PC_TXFIFO stores response transaction from the downstream LPC devices. The PC_ AVAIL status register bit goes high only when a complete response transaction is stored in the PC_TXFIFO.
The Pre_TXFIFO stores an incoming LPC transaction for error checking purposes. In the event of LPC transaction abort or LPC transaction sync error, the transaction is dropped from the Pre_TXFIFO. The transaction is pushed into PC_TXFIFO provided that there is no error, then to eSPI host.