[J-u-boot.git] / doc / README.semihosting

SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright 2014 Broadcom Corporation.
 */

Semihosting is ARM's way of having a real or virtual target communicate
with a host or host debugger for basic operations such as file I/O,
console I/O, etc. Please see
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjjgij.html for more information.

For developing on armv8 virtual fastmodel platforms, semihosting is a
valuable tool since it allows access to image/configuration files before
eMMC or other NV media are available.

There are two main ARM virtual Fixed Virtual Platform (FVP) models,
Versatile Express (VE) FVP and BASE FVP (See
http://www.arm.com/products/tools/models/fast-models/foundation-model.php)
The initial vexpress64 u-boot board created here runs on the VE virtual
platform using the license-free Foundation_v8 simulator. Fortunately,
the Foundation_v8 simulator also supports the BASE_FVP model which
companies can purchase licenses for and contain much more functionality.
So we can, in u-boot, run either model by either using the VE FVP (default),
or turning on CONFIG_BASE_FVP for the more full featured model.

Rather than create a new armv8 board similar to armltd/vexpress64, add
semihosting calls to the existing one, enabled with CONFIG_SEMIHOSTING
and CONFIG_BASE_FVP both set. Also reuse the existing board config file
vexpress_aemv8a.h but differentiate the two models by the presence or
absence of CONFIG_BASE_FVP. This change is tested and works on both the
Foundation and Base fastmodel simulators.

The semihosting code adds a command:

  smhload <image> <address> [env var]

That will load an image from the host filesystem into RAM at the specified
address and optionally store the load end address in the specified
environment variable.
Commit	Line	Data
83d290c5	1	SPDX-License-Identifier: GPL-2.0+
261d2760 DR	2	/*
261d2760 DR	3	* Copyright 2014 Broadcom Corporation.
261d2760 DR	4	*/
	5
	6	Semihosting is ARM's way of having a real or virtual target communicate
	7	with a host or host debugger for basic operations such as file I/O,
	8	console I/O, etc. Please see
	9	http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjjgij.html for more information.
	10
	11	For developing on armv8 virtual fastmodel platforms, semihosting is a
	12	valuable tool since it allows access to image/configuration files before
	13	eMMC or other NV media are available.
	14
	15	There are two main ARM virtual Fixed Virtual Platform (FVP) models,
	16	Versatile Express (VE) FVP and BASE FVP (See
	17	http://www.arm.com/products/tools/models/fast-models/foundation-model.php)
	18	The initial vexpress64 u-boot board created here runs on the VE virtual
	19	platform using the license-free Foundation_v8 simulator. Fortunately,
	20	the Foundation_v8 simulator also supports the BASE_FVP model which
	21	companies can purchase licenses for and contain much more functionality.
	22	So we can, in u-boot, run either model by either using the VE FVP (default),
	23	or turning on CONFIG_BASE_FVP for the more full featured model.
	24
	25	Rather than create a new armv8 board similar to armltd/vexpress64, add
	26	semihosting calls to the existing one, enabled with CONFIG_SEMIHOSTING
	27	and CONFIG_BASE_FVP both set. Also reuse the existing board config file
	28	vexpress_aemv8a.h but differentiate the two models by the presence or
	29	absence of CONFIG_BASE_FVP. This change is tested and works on both the
	30	Foundation and Base fastmodel simulators.
	31
202a674b	32	The semihosting code adds a command:
261d2760	33
202a674b	34	smhload <image> <address> [env var]
261d2760	35
202a674b LW	36	That will load an image from the host filesystem into RAM at the specified
	37	address and optionally store the load end address in the specified
	38	environment variable.