From 93649b122e354341e2556173f2a427c94cb6a8d6 Mon Sep 17 00:00:00 2001 From: Vadim Bendebury Date: Fri, 22 Apr 2016 07:03:43 -0700 Subject: google/gru: Determine Board ID based on the input voltage of ADC1 The Board ID on the Gru family of boards is determined by reading the voltage from a resistor divider, each hardware revision is supposed to have a unique resistor ratio, which allows to distinctly tell between different Board ID. While the long time approach to mapping resistor ratios (and voltages) into Board ID remains under discussion, we know for sure the values for Proto 1 and Proto 2. Let's just use them for now. Since Board ID can be queried multiple times during boot, ideally it should be read once and placed in the coreboot table to be available to all coreboot stages. For now we just cache it so that at least during the same stage the ADC has to run only once. BRANCH=None BUG=chrome-os-partner:51537 TEST=verified that the voltage reading on Proto 1 is as expected, and Board ID 0 is reported. Change-Id: I94bc7fc235dae4155feb6ca35b5ef0ab20c3ec9c Signed-off-by: Patrick Georgi Original-Commit-Id: bb4064d0af8174b6ae247cdad9378b7f4e5f22ba Original-Change-Id: I105ea97f8862b5707b582904c6f2e3e9406a0f07 Original-Signed-off-by: Vadim Bendebury Original-Reviewed-on: https://chromium-review.googlesource.com/340428 Original-Reviewed-by: Patrick Georgi Reviewed-on: https://review.coreboot.org/14722 Tested-by: build bot (Jenkins) Reviewed-by: Stefan Reinauer --- src/mainboard/google/gru/Makefile.inc | 3 --- src/mainboard/google/gru/boardid.c | 37 +++++++++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+), 3 deletions(-) diff --git a/src/mainboard/google/gru/Makefile.inc b/src/mainboard/google/gru/Makefile.inc index da615132a8..a209d1bdf3 100644 --- a/src/mainboard/google/gru/Makefile.inc +++ b/src/mainboard/google/gru/Makefile.inc @@ -13,16 +13,13 @@ ## GNU General Public License for more details. ## -bootblock-y += boardid.c bootblock-y += bootblock.c bootblock-y += chromeos.c bootblock-y += memlayout.ld bootblock-y += reset.c -verstage-y += boardid.c verstage-y += chromeos.c verstage-y += memlayout.ld -verstage-y += memlayout.ld verstage-y += reset.c romstage-y += boardid.c diff --git a/src/mainboard/google/gru/boardid.c b/src/mainboard/google/gru/boardid.c index f62fe97226..5f030adf01 100644 --- a/src/mainboard/google/gru/boardid.c +++ b/src/mainboard/google/gru/boardid.c @@ -16,9 +16,46 @@ #include #include #include +#include + +/* + * This matches two Kevin prototypes, needs to be sorted out with HW engs to + * have more regular mapping between the voltage and board ID. + */ +static const int board_id_readings[] = { 42, 120 }; + +/* + * The ADC produces a 10 bit value, the resistor accuracy is 1%, let's leave + * 2% room for error on both sides, total variation would be 4%, which is + * approximately 40 points with a 10 bit ADC. The hardware specification + * guarantees valid readings to be at least 64 bits (2^6) apart. + */ +#define ACCEPTABLE_DELTA (int)(1024 * .02) uint8_t board_id(void) { + static int cached_board_id = -1; + int i; + int adc_reading; + + if (cached_board_id != -1) + return cached_board_id; + + adc_reading = get_saradc_value(1); + for (i = 0; i < ARRAY_SIZE(board_id_readings); i++) { + int delta = board_id_readings[i] - adc_reading; + + if ((delta < ACCEPTABLE_DELTA) && (delta > -ACCEPTABLE_DELTA)) { + printk(BIOS_DEBUG, "ADC reading %d, " + "expected value %d board ID %d\n", + adc_reading, delta + adc_reading, i); + cached_board_id = i; + return i; + } + } + + printk(BIOS_ERR, "Unmatched ADC reading of %d, using Board ID of 0\n", + adc_reading); return 0; } -- cgit v1.2.3