NS9750 - Training Hardware

1. NS9750 - Training Hardware

2. 1284

3. Traffic Flow Note: Traffic direction in the 1284 is classified as either forward or reverse. The forward direction is equivalent to NS9750 Receive. Likewise, the reverse direction is equivalent to NS9750 Transmit.

4. 1284 Overview • Provides asynchronous and bi-directional parallel communications between a PC, or other host, and a printer. • NS9750 supported 1284 modes: Compatibility, Nibble, Byte, ECP. • NS9750 operates as a slave (peripheral) device only. • Compatibility: • A byte-wide single direction connection from the host to the peripheral. • The default mode of operation. • Backwards compatible with many existing devices. • Nibble: • A nibble-wide single direction connection from the peripheral to the host.

5. 1284 Overview • Byte: • A byte-wide single direction connection from the peripheral to the host. • ECP: • A byte-wide bi-directional connection between the host and peripheral. • Distinguishes between command and data transfers. • More efficient, but more complex, method of sharing data than using either a (compatibility – nibble) or (compatibility – byte) combination. • Note: • No need for a user to use both nibble and byte modes. • The byte mode is slightly less complicated to use.

6. Modes of Operation • Two primary modes of communications between the 1284 and the rest of the chip (DMA & CPU). • DMA: • Establish 4 DMA channels in the BBUS DMA Controller. These channels connect directly to the four primary FIFOs. • Ch9 (FWD CMD) : 10 (REV CMD) : 11 (FWD DATA) : 12 (REV DATA) • Allocate corresponding channel buffers • Configure corresponding control registers • Not an interrupt driven data flow between the 1284 and the BBUS. • Can mask all the interrupts in the Status and Control Register • Can limit the size of receive (forward) DMA buffers. (DMA Control Reg) • Recommended for most customers. • Provides a more powerful and higher performance interface into the 1284.

7. Modes of Operation • CPU: • The CPU can directly access the 4 primary FIFOs . • FIFO locations are located at addresses (0x9040_000C – 0x9040_0020) • The CPU requires the use of interrupts to move data through the interface. • Requires more polling of the FIFOs to ensure that they do not overrun / underrun. The DMA can handle this automatically. • Recommended for debug purposes. • Requires less configuration work in the rest of the chip. • Does require a more intimate knowledge of incoming data in order to set appropriate thresholds for interrupt triggerable events.

8. 1284 Sample Initialization • Bbus Utility block: • Clear the Bbus Utility and 1284 module reset (Master Reset) • Configure GPIO pins (GPIO Configuration Registers) • Bbus Bridge block: • Enable layered interrupts (Bbus Bridge Interrupt Enable) • 1284: • Set 1284 pins to ‘1’ before initialization (Port Control) • Set general user settings (General Configuration) • Clear any spurious received interrupts (Interrupt Status & Control) • Set appropriate interrupt mask bits (Interrupt Status & Control) • Set Fwd. Data/CMD Max Buffer size & byte gap time • CPU Mode -> set Max buffer to 16’hFFFF (Fwd. DMA Control)

9. 1284 Sample Initialization • 1284 (cont): • Set Port Granularity to ‘1’ initially before configuring the registers. Set to ‘0x19’ before traffic flow. (Granularity) • Set buffer for reverse ID transfers (Feature b) • Set Negotiation Start detect int enable (Interrupt Enable) • Disable open drain. Enable reverse request. (Extended Control) • Set Buffer Thresholds. Enable printer port. (Feature A) • Enable desired features (Master Enable)

10. 1284 Timing

11. Hints & Kinks • Which interrupts are essential even in DMA mode? • VCM1 (Interrupt Status & Control) is an aggregate of 1284 core interrupts • Negotiation Start (STI) indicates a new transfer mode has begun. • Pin Select (STI) is an aggregate of the PIT register. • N_init edge detect (PIT) indicates that data flow has reversed in ECP mode. • How can I figure out which is the active data transfer mode? • When negotiating into a new mode the IEEE 1284 Extensibility Value is placed on the data line. This value identifies the mode. It is important to note that compatability mode does not have such a value. This is because it is the default mode. Therefore, the 1284 is in compatability mode when it is not in another mode. It should also be pointed out the 1284 cannot negotiate into a mode except from compatability mode.

12. Hints & Kinks • How is traffic classified as either data or command? • During an ECP transfer a value of ‘1’ on the HostAck (nAutoFd) wire indicates a data transfer. A ‘0’ indicates a command transfer. • So what exactly is command traffic anyway? • There are two possible commands that can be sent: run-length encoding (rle) compression and channel address. Bit [7] of the command is used to select the type of command. ( 0 -> compression : 1 -> channel address) • Rle Compression: The next byte is repeated (bits [6:0] + 1) times and put in the appropriate FIFO. Note: The user must make sure that the next byte transferred is classified as data in order for it to replicated in the data FIFO. • Channel Address: Bits [6:0] of the current byte are stored as a channel address which can be read in the ECA register. • What are other sources of information? • www.ieee.org Standards # 1284-1994. • NS9775 user’s manual.