|C H A P T E R 1|
SBus Cards and FCode
Each SBus card must have a PROM whose contents identify the device and its characteristics.
The SBus card's PROM may also include an optional software driver that lets you use the card as a boot device or a display device during booting.
In addition to designing hardware, the process of developing SBus devices may include writing, testing, and installing FCode drivers for the device. These drivers, if present, perform three functions:
In practice, these functions overlap substantially. The same code needed by the system boot PROM usually serves to significantly test the device as well, although additional code may be desired to fully verify proper behavior of the device. The PROM code is used before and during the boot sequence. After the boot sequence finishes, and while not using the OpenBoot FORTH Monitor, most SBus device use is through Solaris drivers.
SBus device PROMs must be written in the FCode programming language, which is similar to ANS Forth. FCode is described in more detail in Chapter 3.
This chapter includes the following sections:
An FCode PROM begins at address 0 in the SBus card's physical address space. Its size can range from 30 bytes up to 32Kbytes. Typical sizes are 60 bytes (for a simple card that identifies itself but does not need a driver) and 5 to 15Kbytes (for a card with a boot driver). It is good practice to make FCode boot drivers as short as is practical.
An FCode PROM must be organized as follows:
For each SBus slot, the FCode program is interpreted during boot as follows:
An FCode PROM must identify its device. This identification must include, at a minimum, the device name used to link the device to its Solaris driver. Identification information may include additional characteristics of the device for the benefit of the operating system and the CPU boot PROM.
In most systems, the CPU's FCode interpreter will store each device's identification information in a device tree that has a node for each device. Each device node has a property list that identifies and describes the device. The property list is created as a result of interpreting the program in the FCode PROM.
Each property must have a name and a value. The name is a string and the value is an array of bytes, which may encode strings, numbers, and various other data types.
See Chapter 7 for more information.
Many FCode programs create executable routines, called colon definitions (or methods) that typically read from and write to device locations to control device functions. These definitions are also stored in the device tree node for that device.
Once defined, these routines may typically be executed under any of the following circumstances: