Intel SA-1100 manual MCP Transmit and Receive Fifo Operation

Peripheral Control Module

If the input portion of the audio codec is enabled, when the counter reaches zero, a sample and A-to-D conversion is made and the converted value is placed within the correct field of the codec’s serial shift register for transmission back to the MCP in the next data frame. If the output portion of the audio codec is enabled, an audio data value is taken from the received data supplied by the MCP and is used for a D-to-A conversion. Data used in the D-to-A conversion is always taken from the previous MCP input frame. If no new data is available within the MCP’s audio transmit FIFO since the last D-to-A conversion, then the same data is used again (causing audio distortion).

Samples and conversions occur twice in the preceding figure. However, while the counter is decrementing for the third time, the CPU disables the audio codec by issuing another control register write, represented by the “Dis” data frame on TXD4. The SFRM pulse following the write causes the disable to take effect, and the MCP and codec’s audio sample rate counters are stopped and reset to their modulus values.

The MCP and the codec’s audio sample rate counters must be enabled coherently so that synchronization is achieved between the two. This is accomplished by first programming both the MCP and codec’s sample rate modulus values, then performing a codec control register write to enable the audio sampling rate counter within the codec. The MCP automatically decodes a write to the audio codec input and output enable bits, and enables the MCP’s audio sample rate counter at the same time as the codec’s counter to ensure synchronization.

The UCB1100 and UCB1200 each have an individual data valid bit for audio and telecom A/D samples. Whenever these bits are set in the data frame returned from the codec to the MCP, the audio and telecom data is taken from the frame and placed in their respective receive FIFOs. The UCB1100 and UCB1200 have two different modes of operation to control the setting of the audio and telecom data valid bits. In the first mode, a data valid bit is set any time a frame contains “reliable” data ( the codec is enabled and at least one A-to-D sample has been taken). In this mode, once the data valid bit is set, it remains set until the codec A-to-D input is disabled. In the second mode, the codec only sets the data valid bit corresponding to a new A-to-D sample. Once the data is transmitted to the MCP within a receive data frame, the data valid bit is reset to zero for subsequent data frames until a new A-to-D sample is triggered.

11.12.1.3MCP Transmit and Receive FIFO Operation

The MCP contains four 8-entry x 16-bit FIFOs: one for audio and one for telecom A-to-D samples received by the MCP, as well as one for audio and one for telecom D-to-A conversions transmitted to the codec. For the remainder of this description, references made to the audio codec also apply to the telecom portion of the codec and MCP.

For each incoming data frame, if the audio data valid bit is set, the 16-bit audio A-to-D sample is extracted and placed in the audio receive FIFO. Note that the MCP also supports a mode in which the audio data valid bit is ignored after the first conversion has been saved to the FIFO, and the MCP’s audio sample rate counter is used to signal when a new A-to-D sample has been taken and is available within the incoming frame. Audio data is transferred from the incoming data frames to the receive FIFO only if the audio enable bit is set within the MCP’s status register.

The MCP’s audio and telecom sample rate counters are used to trigger when new D/A conversions are to be transmitted to the codec. The user should take care in ensuring sample rate counters in the MCP are synchronized with the respective sample rate counters in the codec as described in preceding sections. When the audio enable status bit transitions from a 0 to a 1 within the MCP status register, the next available entry of data is taken from the audio transmit FIFO and is placed within the correct field in the MCP’s serial shifter. This value is then continuously transferred by the MCP in each data frame to the codec. The codec uses the value only when its audio sample rate counter decrements to zero. After the audio D-to-A conversion is made, both the codec and the MCP’s audio sample rate counters reload with their modulus values. This reload triggers the audio transmit FIFO to transfer the next available entry of data to the MCP’s serial shifter. Again, this value is continuously transmitted to the codec in each data frame until it is used in the next audio D-to-A conversion.

SA-1100 Developer’s Manual 11-149