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buspirate_spi: add support for hiz output with pullups=off

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When working with low-voltage chips, the internal 10k pull-ups
of the Bus Pirate might be too high. In such cases, it's necessary
to create an external pull-up using lower-value resistors. For this,
you can use the 'hiz' parameter.  This way, the Bus Pirate will
operate as an open drain with 'pullups=off'

So, why not just use the 'pullups=on' option for this scenario? I'm
trying to prevent a very typical human error in the training sessions
I conduct.

For example, in the previous session, a user might have left the VPU
(vextern) connected to 5V, and now they need to access a 1.8V chip.
If 'pullups=on' is used, the following will happen:
5V (VPU) --> CD4060 --> 2K (internal Bus Pirate) --> MOSI target chip.
By having the option to set a 'hiz=on', this can be avoided. Since the
pull-ups will remain deactivated while the Bus Pirate will function in
an open-drain mode

Return init error for invalid values of pullups, hiz, psus. Previously,
invalid values of the params pullups, hiz, psus were handled as "off"
(i.e. disabled). This created a potential human error when users were
running flashrom with e.g. pullups=1 and expected pullups to be on,
while the value 1 was handled as invalid and off.

Change-Id: I6d9909b23782ef3fcb1428fd127dae0d6b211855
Signed-off-by: David Reguera Garcia <dreg@rootkit.es>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/79299
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
This commit is contained in:
David Reguera Garcia 2023-12-07 03:20:51 +01:00 committed by Anastasia Klimchuk
parent 360d965ce7
commit 0dbf2ded28
2 changed files with 45 additions and 10 deletions
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47
buspirate_spi.c
View File

@ -325,6 +325,7 @@ static int buspirate_spi_init(const struct programmer_cfg *cfg)
int spispeed = 0x7;
int serialspeed_index = -1;
int ret = 0;
bool hiz = false;
bool pullup = false;
bool psu = false;
bool aux = true;
@ -370,23 +371,49 @@ static int buspirate_spi_init(const struct programmer_cfg *cfg)
tmp = extract_programmer_param_str(cfg, "pullups");
if (tmp) {
if (strcasecmp("on", tmp) == 0)
if (strcasecmp("on", tmp) == 0) {
pullup = true;
else if (strcasecmp("off", tmp) == 0)
} else if (strcasecmp("off", tmp) == 0) {
; // ignore
else
msg_perr("Invalid pullups state, not using them.\n");
} else {
msg_perr("Invalid pullups state. Use on/off.\n");
free(tmp);
return 1;
}
}
free(tmp);
tmp = extract_programmer_param_str(cfg, "hiz");
if (tmp) {
if (strcasecmp("on", tmp) == 0) {
hiz = true;
} else if (strcasecmp("off", tmp) == 0) {
if (pullup) {
msg_perr("Invalid combination: pullups=on & hiz=off at same time is not possible.\n");
free(tmp);
return 1;
} else {
; // ignore
}
} else {
msg_perr("Invalid hiz state. Use on/off.\n");
free(tmp);
return 1;
}
}
free(tmp);
tmp = extract_programmer_param_str(cfg, "psus");
if (tmp) {
if (strcasecmp("on", tmp) == 0)
if (strcasecmp("on", tmp) == 0) {
psu = true;
else if (strcasecmp("off", tmp) == 0)
} else if (strcasecmp("off", tmp) == 0) {
; // ignore
else
msg_perr("Invalid psus state, not enabling.\n");
} else {
msg_perr("Invalid psus state. Use on/off.\n");
free(tmp);
return 1;
}
}
free(tmp);
@ -692,9 +719,9 @@ static int buspirate_spi_init(const struct programmer_cfg *cfg)
/* Set SPI config: output type, idle, clock edge, sample */
bp_commbuf[0] = 0x80 | 0xa;
if (pullup) {
if (pullup || hiz) {
bp_commbuf[0] &= ~(1 << 3);
msg_pdbg("Pull-ups enabled, so using HiZ pin output! (Open-Drain mode)\n");
msg_pdbg("Pull-ups or HiZ enabled, so using HiZ pin output! (Open-Drain mode)\n");
}
ret = buspirate_sendrecv(bp_commbuf, 1, 1);
if (ret)

8
doc/classic_cli_manpage.rst
View File

@ -772,6 +772,14 @@ where ``state`` can be ``on`` or ``off``.
More information about the Bus Pirate pull-up resistors and their purpose is available
`in a guide by dangerousprototypes <http://dangerousprototypes.com/docs/Practical_guide_to_Bus_Pirate_pull-up_resistors>`_.
When working with low-voltage chips, the internal 10k pull-ups of the Bus Pirate might be too high. In such cases, it's necessary to create an external pull-up using lower-value resistors.
For this, you can use the ``hiz`` parameter. This way, the Bus Pirate will operate as an open drain. Syntax is::
flashrom -p buspirate_spi:hiz=state
where ``state`` can be ``on`` or ``off``.
The state of the Bus Pirate power supply pins is controllable through an optional ``psus`` parameter. Syntax is::
flashrom -p buspirate_spi:psus=state