From OR1K

Introduction

The OpenRISC 1000 port of the newlib library aims to provide a library to provide support for running on bare-metal hardware without an operating system. It is also used when running the GNU toolchain regression suite.

The library is automatically linked when using the newlib version of the GCC compiler (or32-elf-gcc). The target board is specified by -mboardname. If not board is specified, the default (-mor1ksim) is suitable for use with Or1ksim.

Port acknowledgements

This original port was for newlib 1.13.0 by Jacob Bower, then of Imperial College, London.

The port was completely rewritten and tested for newlib 1.18.0 by Jeremy Bennett of Embecosm. Further information is availble in Embecosm Application Note 9 Howto: Porting Newlib: A Simple Guide, which explains in full detail how the port for the OpenRISC 1000 architecture was done.

The port was subsequently extended by Julius Baxter to make support of multiple boards much more flexible.

OpenRISC support library

To assist with using features of the OpenRISC processor such as exceptions, interrupts and timers, a support library has been implemented.

This library also provides support for particular boards in ORPSoC.

Support library functions

These functions are implemented in the or1k-support.c and or1k-support-asm.S files in the newlib/libc/machine/or32 path in the newlib port directory. The header, or1k-newlib-support.h is found in the newlib/libc/machine/or32/include path. Note that this header and the OR1K spr-defs.h header are installed also in the /install_path/or32-elf/include path.

They are accessible via the inclusion of the following header.

#include <or1k-support.h>

The following functions are provided

Function Name	Arguments	Description	Return value
`or1k_interrupt_handler_add`	`int irq, void(function_name)(void)`	Install function_name as handler for interrupt at IRQ `irq`	none
`or1k_interrupt_enable`	`int irq`	Enable generation interrupt at IRQ irq in PICMR	none
`or1k_interrupt_disable`	`int irq`	Disable generation of interrupt at IRQ irq in PICMR	none
`or1k_exception_handler_add`	`int vector, void(function_name)(void)`	Install function_name as handler for vector at address (vector*0x100)	none
`or1k_mtspr`	`unsigned long int spr, unsigned long int value`	Write SPR[spr] = value	none
`or1k_mfspr`	`unsigned long int spr`	Read SPR[spr]	SPR[spr]
`or1k_report`	`unsigned long int value`	Simulator report function with l.nop 0x2	none
`or1k_icache_enable`	`void`	Enable instruction cache in SR	none
`or1k_icache_disable`	`void`	Disable instruction cache in SR	none
`or1k_icache_flush`	`unsigned long addr`	Flush addr from instruction cache	none
`or1k_dcache_enable`	`void`	Enable data cache in SR	none
`or1k_dcache_disable`	`void`	Disable data cache in SR	none
`or1k_dcache_flush`	`unsigned long addr`	Flush addr from data cache	none
`or1k_immu_enable`	`void`	Enable instruction MMU in SR	none
`or1k_immu_disable`	`void`	Disable instruction MMU in SR	none
`or1k_dmmu_enable`	`void`	Enable data MMU in SR	none
`or1k_dmmu_disable`	`void`	Disable data MMU in SR	none
`or1k_timer_init`	`unsigned int hz`	Initialise timer to count at hz hertz, reset tick counter, install handler	none
`or1k_timer_enable`	`void`	Start timer, enable timer interrupt in SR	none
`or1k_timer_disable`	`void`	Stop timer interrupts	none
`or1k_timer_get_ticks`	`void`	Read tick counter value	tick counter
`or1k_timer_reset_ticks`	`void`	Reset tick counter value	none

Contributions are welcome to help fix and improve this support library.

Feel free to post any suggestions or offers to assist the project to the OpenRISC forum or the mailing lists.

TODO

Functions still missing: interrupt acknowledge/clear function to clear bit in PICSR, cache region flush, MMU map function.

Board support details

The OpenRISC portion of libgloss provides a simple way of adding support for boards by way of linking in a small library containing some values used at run-time to configure the system. Each board has its own path and libboard.a in the /install_path/or32-elf/lib/boards/boardname directory. The boardname above should correspond to a directory under this path.

Libgloss also implements system calls, and at present only read and write system calls are supported via the UART.

In the version currently in the repository, a handful of boards and the or1ksim architectural simulator are supported.

Board	Description
or1ksim	or1ksim simulator, no peripherals
or1ksim-uart	or1ksim simulator with a UART
ordb1a3pe1500	ORSoC dedvelopment board 1, A3PE1500 part, as in ORPSoC
ml501	Xilinx ML501 board, as in ORPSoC
orpsocrefdesign	ORPSoC reference design

For example, to compile with support for the ordb1a3pe1500 board, one would pass the following options at compile-time.

or32-elf-gcc -mboard=ordb1a3pe1500

Each libboard.a defines the following symbols:

Symbol	Description
_board_mem_base	Base of main memory
_board_mem_size	Size of main memory
_board_clk_freq	Frequency in hertz of CPU clock, also presumed as UART clock
_board_uart_base	Base address of a UART 16550 peripheral
_board_uart_baud	Desired buad rate for UART
_board_uart_IRQ	IRQ number of UART

Adding support for a new board

Adding additional boards (without recompiling and installing the toolchain) is as simple as creating a creating a libboard.a with the appropriate symbols set to the right values and placing it in the /install_path/or32-elf/lib/boards/boardname directory. The boardname should be the same as the one used when passing the -mboard=boardname to the compiler.

To create this libboard.a see examples of the existing boardname.S files in the newlib-1.x.0/libgloss/or32 path in the newlib port source.

For example, the ml501 board's code is in the newlib-1.x.0/libgloss/or32/ml501.S file and is as follows:

/*
 * Define symbols to be used during startup - file is linked at compile time
 *
 */
.global _board_mem_base
.global _board_mem_size
.global _board_clk_freq 

_board_mem_base:	.long	0x0
_board_mem_size:	.long	0x800000

_board_clk_freq:	.long	66666666 

/* Peripheral information - Set base to 0 if not present*/
.global _board_uart_base
.global _board_uart_baud
.global _board_uart_IRQ
	
_board_uart_base:	.long	0x90000000
_board_uart_baud:	.long	115200
_board_uart_IRQ:	.long	2

This file should be assembled and archived, and then placed into the correct install path as mentioned above.

Apr	MAY	Jun
	14
2011	2012	2013

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