3.8. Test Chip IP

Chipyard includes a Test Chip IP library which provides various hardware widgets that may be useful when designing SoCs. This includes a SimTSI, Block Device Controller, TileLink SERDES, TileLink Switcher, TileLink Ring Network, and UART Adapter.

3.8.1. SimTSI

The SimTSI and TSIToTileLink are used by tethered test chips to communicate with the host processor. An instance of RISC-V frontend server running on the host CPU can send commands to the TSIToTileLink to read and write data from the memory system. The frontend server uses this functionality to load the test program into memory and to poll for completion of the program. More information on this can be found in Chipyard Boot Process.

3.8.2. Block Device Controller

The block device controller provides a generic interface for secondary storage. This device is primarily used in FireSim to interface with a block device software simulation model. The default Linux configuration in firesim-software

To add a block device to your design, add the WithBlockDevice config fragment to your configuration.

3.8.3. TileLink SERDES

The TileLink SERDES in the Test Chip IP library allow TileLink memory requests to be serialized so that they can be carried off chip through a serial link. The five TileLink channels are multiplexed over two SERDES channels, one in each direction.

There are three different variants provided by the library, TLSerdes exposes a manager interface to the chip, tunnels A, C, and E channels on its outbound link, and tunnels B and D channels on its inbound link. TLDesser exposes a client interface to the chip, tunnels A, C, and E on its inbound link, and tunnels B and D on its outbound link. Finally, TLSerdesser exposes both client and manager interface to the chip and can tunnel all channels in both directions.

For an example of how to use the SERDES classes, take a look at the SerdesTest unit test in the Test Chip IP unit test suite.

3.8.4. TileLink Switcher

The TileLink switcher is used when the chip has multiple possible memory interfaces and you would like to select which channels to map your memory requests to at boot time. It exposes a client node, multiple manager nodes, and a select signal. Depending on the setting of the select signal, requests from the client node will be directed to one of the manager nodes. The select signal must be set before any TileLink messages are sent and be kept stable throughout the remainder of operation. It is not safe to change the select signal once TileLink messages have begun sending.

For an example of how to use the switcher, take a look at the SwitcherTest unit test in the Test Chip IP unit tests.

3.8.5. TileLink Ring Network

TestChipIP provides a TLRingNetwork generator that has a similar interface to the TLXbar provided by RocketChip, but uses ring networks internally rather than crossbars. This can be useful for chips with very wide TileLink networks (many cores and L2 banks) that can sacrifice cross-section bandwidth to relieve wire routing congestion. Documentation on how to use the ring network can be found in The System Bus. The implementation itself can be found here, and may serve as an example of how to implement your own TileLink network with a different topology.

3.8.6. UART Adapter

The UART Adapter is a device that lives in the TestHarness and connects to the UART port of the DUT to simulate communication over UART (ex. printing out to UART during Linux boot). In addition to working with stdin/stdout of the host, it is able to output a UART log to a particular file using +uartlog=<NAME_OF_FILE> during simulation.

By default, this UART Adapter is added to all systems within Chipyard by adding the WithUART and WithUARTAdapter configs.

3.8.7. SPI Flash Model

The SPI flash model is a device that models a simple SPI flash device. It currently only supports single read, quad read, single write, and quad write instructions. The memory is backed by a file which is provided using +spiflash#=<NAME_OF_FILE>, where # is the SPI flash ID (usually 0).

3.8.8. Chip ID Pin

The chip ID pin sets the chip ID for the chip it is added to. This is most useful in multi-chip configs. The pin value is driven by the chip ID value set in the harness binder and the chip ID value can be read through MMIO at the address 0x2000 by default.

The pin can be added to a system with the testchipip.soc.WithChipIdPin config. The pin width and MMIO address are parameterizable and can be set by passing ChipIdPinParams as an argument to the config. The width can additionally be set using the testchipip.soc.WithChipIdPinWidth config.