Chapter 5. Configuring And Activating The Port
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## Chapter 5. Configuring And Activating The Port

The Z85230 driver provides helper functions and tables to load the port registers on the Z8530 chips. When programming the register settings for a channel be aware that the documentation recommends initialisation orders. Strange things happen when these are not followed.

`z8530_channel_load` takes an array of pairs of initialisation values in an array of u8 type. The first value is the Z8530 register number. Add 16 to indicate the alternate register bank on the later chips. The array is terminated by a 255.

The driver provides a pair of public tables. The z8530_hdlc_kilostream table is for the UK 'Kilostream' service and also happens to cover most other end host configurations. The z8530_hdlc_kilostream_85230 table is the same configuration using the enhancements of the 85230 chip. The configuration loaded is standard NRZ encoded synchronous data with HDLC bitstuffing. All of the timing is taken from the other end of the link.

When writing your own tables be aware that the driver internally tracks register values. It may need to reload values. You should therefore be sure to set registers 1-7, 9-11, 14 and 15 in all configurations. Where the register settings depend on DMA selection the driver will update the bits itself when you open or close. Loading a new table with the interface open is not recommended.

There are three standard configurations supported by the core code. In PIO mode the interface is programmed up to use interrupt driven PIO. This places high demands on the host processor to avoid latency. The driver is written to take account of latency issues but it cannot avoid latencies caused by other drivers, notably IDE in PIO mode. Because the drivers allocate buffers you must also prevent MTU changes while the port is open.

Once the port is open it will call the rx_function of each channel whenever a completed packet arrived. This is invoked from interrupt context and passes you the channel and a network buffer (struct sk_buff) holding the data. The data includes the CRC bytes so most users will want to trim the last two bytes before processing the data. This function is very timing critical. When you wish to simply discard data the support code provides the function `z8530_null_rx` to discard the data.

To active PIO mode sending and receiving the `z8530_sync_open` is called. This expects to be passed the network device and the channel. Typically this is called from your network device open callback. On a failure a non zero error status is returned. The `z8530_sync_close` function shuts down a PIO channel. This must be done before the channel is opened again and before the driver shuts down and unloads.

The ideal mode of operation is dual channel DMA mode. Here the kernel driver will configure the board for DMA in both directions. The driver also handles ISA DMA issues such as controller programming and the memory range limit for you. This mode is activated by calling the `z8530_sync_dma_open` function. On failure a non zero error value is returned. Once this mode is activated it can be shut down by calling the `z8530_sync_dma_close`. You must call the close function matching the open mode you used.

The final supported mode uses a single DMA channel to drive the transmit side. As the Z85C30 has a larger FIFO on the receive channel this tends to increase the maximum speed a little. This is activated by calling the `z8530_sync_txdma_open` . This returns a non zero error code on failure. The `z8530_sync_txdma_close` function closes down the Z8530 interface from this mode.

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