MPC5566 Runtimes
================

Runtimes Supported
------------------

* Light
* Light-Tasking
* Embedded

Targets Supported
-----------------

NXP MPC5566 Power Architecture e200z6 core (but upwards-compatible with
the e500 series)

System Clocks
-------------

See package System.BB.Board_Parameters (`s-bbbopa.ads`) in the gnat
directory for the clock frequency declaration.

Startup Code
------------

There are three assembly language files for the startup code, one each
for executing from RAM, BAM (the boot assist module), or FLASH. These
are `start-ram.S`, `start-bam.S`, and `start-flash.S` respectively.

Selection of the startup code is controlled indirectly by a scenario
variable named "Loader." This scenario variable is declared in an xml
file (runtime.xml) read by gprbuild automatically and used to specify
linker switches and scripts. These linker scripts select the startup
code by specifying the entry point using the names defined in the
assembly files.

The assembly file `setup.S` is called by these three assembly files above
to enable the SPE and the overflow, division by zero, and invalid
exceptions.

Another assembly file, `setup_pll.S`, is called by `start-bam.S` and
`start-flash.S` to configure the PLL.

Note that the body of package System.Machine_Reset is in
`gnat/s-macres.adb`.

Interrupts
----------

The package Ada.Interrupts.Names is located in the gnat directory
(`gnat/a-intnam.ads`).

See the package body for System.BB.Board_Support (`s-bbbosu.adb`) in the
gnat directory for board configuration for interrupts.

See package System.BB.Parameters (`gnat/s-bbpara.ads`) for the number of
interrupts defined. The runtime supports at most 128 interrupts external
interrupts and 8 non external. If you have more interrupts, you need to
change the values used in the declaration of subtype Interrupt_Range in
that package.

Memory Layout
-------------

The memory layout is controlled by the scenario variable named "Loader"
described above that specifies linker switches and scripts. These
scripts, located in the ld/ directory, specify the layout corresponding
to the scenario value, as follows:

* EXTRAM : `ram.ld`
* BAM    : `bam.ld`
* FLASH  : `flash.ld`

The default is EXTRAM.

Resources Used
--------------

The Ravenscar runtime libraries use the time base and decrementer core
registers to implement Ada semantics for time, i.e., delay statements
and package Ada.Real_Time. See the package body for
System.BB.Board_Support in the file `gnat/s-bbsuti.adb`. Note that these
registers are 32-bits wide, so although the underlying time base value
is 64-bits, the value must be read in two separate instructions, that
is, non-atomically, and then combined. This results in the possibility
of a race condition in which the upper half changes after being read,
apart from when the lower half is read. To deal with that race condition
a loop is used, but note that this requires multiple reads of the two
registers. See function Read_Clock in that package for the loop.

The runtime libraries provide a minimal version of package Ada.Text_IO
supporting character- and string-based input and output routines. The
bodies of the Ada.Text_IO routines call through to a device-specific I/O
package named System.Text_IO. See the package body in the file
s-textio.adb in the gnat directory. The default console is available via
the enhanced serial communication interface (eSCI) module A, with line
configuration (baud rate etc.) set to one start bit, eight data bits, no
parity and one stop bit, and a baud rate equal to the system clock
frequency divided by 1250.