Implementation of the touch-screen calibration utility. More...

#include "ra8_touch_cal.h"
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include "ra8_attributes.h"
#include "ra8_err.h"

Include dependency graph for ra8_touch_cal.c:

Data Structures
struct	internal_lsq_sums_t
	Accumulated least-squares sums driving the calibration solve. More...

Enumerations
enum	mat3_idx_t : uint8_t { k_m3_00 = 0U , k_m3_01 = 1U , k_m3_02 = 2U , k_m3_10 = 3U , k_m3_11 = 4U , k_m3_12 = 5U , k_m3_20 = 6U , k_m3_21 = 7U , k_m3_22 = 8U , k_m3_len = 9U }
	Row-major flat indices of a 3x3 matrix (a[r*3+c]). More...
enum	affine_coeff_idx_t : uint8_t { k_coeff_a = 0U , k_coeff_b = 1U , k_coeff_c = 2U , k_coeff_d = 3U , k_coeff_e = 4U , k_coeff_f = 5U }
	Affine calibration coefficient indices (a..f). More...
enum	internal_const_t : uint32_t { k_internal_centre_div = 2U , k_internal_byte_mask = 0xFFU , k_internal_byte_shift_8 = 8U , k_internal_byte_shift_16 = 16U , k_internal_byte_shift_24 = 24U , k_internal_crc32_init = 0xFFFFFFFFU , k_internal_crc32_poly = 0xEDB88320U , k_internal_bits_per_byte = 8U }
	Module-private numeric constants (no magic numbers). More...

Functions
static void	internal_pack_le32 (uint8_t *dst, uint32_t word)
	Pack a 32-bit little-endian word into a byte buffer.
static uint32_t	internal_unpack_le32 (const uint8_t *src)
	Unpack a 32-bit little-endian word from a byte buffer.
static uint32_t	internal_float_to_u32 (float f)
	Bitwise reinterpret a float as a uint32_t.
static float	internal_u32_to_float (uint32_t w)
	Bitwise reinterpret a uint32_t as a float.
static uint32_t	internal_crc32 (const uint8_t *data, size_t len)
	Compute the IEEE 802.3 CRC32 of a byte range.
static void	internal_solve3 (const float a[k_m3_len], const float b[3], float x[3], bool *ok)
	Solve a 3x3 system A * x = b via Cramer's rule.
static int32_t	internal_clip32 (int32_t v, int32_t lo, int32_t hi)
	Clip a value to [lo, hi].
static void	internal_accumulate_sums (const ra8_touch_cal_point_t raw, const ra8_touch_cal_point_t screen, uint8_t n, internal_lsq_sums_t *s)
	Accumulate the 11 least-squares sums over n sample pairs.
ra8_err_t	ra8_touch_cal_compute (const ra8_touch_cal_point_t raw, const ra8_touch_cal_point_t screen, uint8_t n, ra8_touch_cal_matrix_t *out_mtx)
	Compute an affine transform from N target/sample pairs.
ra8_err_t	ra8_touch_cal_run (const ra8_touch_cal_run_cfg_t cfg, ra8_touch_cal_matrix_t out_matrix)
	Drive the on-screen calibration sequence and produce a matrix.
ra8_err_t	ra8_touch_cal_apply (ra8_touch_cal_point_t raw, const ra8_touch_cal_matrix_t matrix, uint16_t screen_width, uint16_t screen_height, ra8_touch_cal_point_t out_screen)
	Apply a calibration matrix to a single raw touch sample.
ra8_err_t	ra8_touch_cal_save (const ra8_touch_cal_matrix_t matrix, uint8_t dst, size_t dst_size)
	Serialise a calibration matrix to a fixed-size byte blob.
ra8_err_t	ra8_touch_cal_load (const uint8_t src, size_t src_size, ra8_touch_cal_matrix_t out_matrix)
	Deserialise a calibration matrix from a byte blob.

Variables
static const float	s_min_det = 1.0e-3F
	Floor for \|det\| below which the normal equations are treated as singular.
static const float	s_round_bias = 0.5F
	Round-to-nearest bias for float->int conversion.

Detailed Description

Implementation of the touch-screen calibration utility.

Tag: [Ring 3 / HAL] {World: NS}

The math here implements the weighted least-squares affine fit from Fang & Chang, "Calibration of Touch Screens for Use with Embedded Systems" (Analog Dialogue 41-08, 2007). For N raw/screen sample pairs the screen-X coefficients (a, b, c) satisfy

[ Sxx Sxy Sx ] [ a ]   [ Sxu ]
[ Sxy Syy Sy ] [ b ] = [ Syu ]
[ Sx  Sy  N  ] [ c ]   [ Su  ]

where the sums run over the N samples. The same 3x3 system with the right-hand side replaced by (Sxv, Syv, Sv) solves for the screen-Y coefficients (d, e, f). The solver is Cramer's rule on the shared coefficient matrix, which keeps the implementation branch-light and avoids dynamic allocation.

Copyright: Copyright (c) 2026 Brighton Sikarskie SPDX-License-Identifier: MIT

Definition in file ra8_touch_cal.c.

Enumeration Type Documentation

◆ affine_coeff_idx_t

enum affine_coeff_idx_t : uint8_t

Affine calibration coefficient indices (a..f).

Enumerator
k_coeff_a	Coeff a.
k_coeff_b	Coeff b.
k_coeff_c	Coeff c.
k_coeff_d	Coeff d.
k_coeff_e	Coeff e.
k_coeff_f	Coeff f.

Definition at line 57 of file ra8_touch_cal.c.

◆ internal_const_t

enum internal_const_t : uint32_t

Module-private numeric constants (no magic numbers).

Enumerator
k_internal_centre_div	Halve to get panel centre.
k_internal_byte_mask	8-bit mask for byte extracts.
k_internal_byte_shift_8	Shift to byte 1.
k_internal_byte_shift_16	Shift to byte 2.
k_internal_byte_shift_24	Shift to byte 3.
k_internal_crc32_init	IEEE 802.3 CRC seed.
k_internal_crc32_poly	IEEE 802.3 reversed polynomial.
k_internal_bits_per_byte	Bits in one byte.

Definition at line 70 of file ra8_touch_cal.c.

◆ mat3_idx_t

enum mat3_idx_t : uint8_t

Row-major flat indices of a 3x3 matrix (a[r*3+c]).

Enumerator
k_m3_00	M3 00.
k_m3_01	M3 01.
k_m3_02	M3 02.
k_m3_10	M3 10.
k_m3_11	M3 11.
k_m3_12	M3 12.
k_m3_20	M3 20.
k_m3_21	M3 21.
k_m3_22	M3 22.
k_m3_len	M3 length.

Definition at line 43 of file ra8_touch_cal.c.

Function Documentation

◆ internal_accumulate_sums()

void internal_accumulate_sums	(	const ra8_touch_cal_point_t *	raw,
		const ra8_touch_cal_point_t *	screen,
		uint8_t	n,
		internal_lsq_sums_t *	s )

static

Accumulate the 11 least-squares sums over n sample pairs.

Pure-data helper extracted from ra8_touch_cal_compute to keep the top-level function within the NASA P10 Rule 4 cap. The arithmetic is bit-identical to the inlined original.

Parameters

[in]	raw	Raw touch samples (length n).
[in]	screen	Screen targets (length n).
[in]	n	Sample count.
[out]	s	Accumulated sums (zero-initialized by the helper).

Precondition: All pointers are non-NULL and n >= 1.; Caller has already validated argument ranges.

Postcondition: s holds the 11 sums over [0, n).; No global state is mutated.

Note: Pure compute helper; safe from any context.

Since: 0.1.0

Definition at line 360 of file ra8_touch_cal.c.

References internal_lsq_sums_t::Su, internal_lsq_sums_t::Sv, internal_lsq_sums_t::Sx, internal_lsq_sums_t::Sxu, internal_lsq_sums_t::Sxv, internal_lsq_sums_t::Sxx, internal_lsq_sums_t::Sxy, internal_lsq_sums_t::Sy, internal_lsq_sums_t::Syu, internal_lsq_sums_t::Syv, and internal_lsq_sums_t::Syy.

Referenced by ra8_touch_cal_compute().

◆ internal_clip32()

int32_t internal_clip32	(	int32_t	v,
		int32_t	lo,
		int32_t	hi )

static

Clip a value to [lo, hi].

See implementation.

Parameters

[in]	v	See implementation.
[in]	lo	See implementation.
[in]	hi	See implementation.

Returns: Result code.

Return values

k_ra8_ok Operation succeeded.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 298 of file ra8_touch_cal.c.

Referenced by ra8_touch_cal_apply().

◆ internal_crc32()

uint32_t internal_crc32	(	const uint8_t *	data,
		size_t	len )

static

Compute the IEEE 802.3 CRC32 of a byte range.

Bit-banged so the function works without depending on ra8_crc.

Parameters

[in]	data	Input bytes.
[in]	len	Number of bytes.

Returns: Final CRC32, post-XOR.

Return values

k_ra8_ok Operation succeeded.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 217 of file ra8_touch_cal.c.

References k_internal_bits_per_byte, k_internal_crc32_init, and k_internal_crc32_poly.

Referenced by ra8_touch_cal_load(), and ra8_touch_cal_save().

◆ internal_float_to_u32()

uint32_t internal_float_to_u32 ( float f )

static

Bitwise reinterpret a float as a uint32_t.

Implemented via memcpy to avoid strict-aliasing UB.

Parameters

[in] f Source float.

Returns: Bit pattern of f.

Return values

k_ra8_ok Operation succeeded.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 168 of file ra8_touch_cal.c.

References memcpy().

Referenced by ra8_touch_cal_save().

◆ internal_pack_le32()

void internal_pack_le32	(	uint8_t *	dst,
		uint32_t	word )

static

Pack a 32-bit little-endian word into a byte buffer.

Parameters

[out]	dst	Destination (4 bytes available).
[in]	word	Value to write.

See implementation.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 118 of file ra8_touch_cal.c.

References k_internal_byte_mask, k_internal_byte_shift_16, k_internal_byte_shift_24, and k_internal_byte_shift_8.

Referenced by ra8_touch_cal_save().

◆ internal_solve3()

void internal_solve3	(	const float	a[k_m3_len],
		const float	b[3],
		float	x[3],
		bool *	ok )

static

Solve a 3x3 system A * x = b via Cramer's rule.

Pure float math. Degenerate (collinear) systems are flagged via the ok out-parameter rather than an error code so the call sites can fold the check into their existing return path.

Parameters

[in]	a	Row-major coefficient matrix (length 9).
[in]	b	Right-hand side (length 3).
[out]	x	Solution vector (length 3).
[out]	ok	Set to true on success, false if \|det\| < s_min_det.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 251 of file ra8_touch_cal.c.

References k_m3_00, k_m3_01, k_m3_02, k_m3_10, k_m3_11, k_m3_12, k_m3_20, k_m3_21, k_m3_22, k_m3_len, and s_min_det.

Referenced by ra8_touch_cal_compute().

◆ internal_u32_to_float()

float internal_u32_to_float ( uint32_t w )

static

Bitwise reinterpret a uint32_t as a float.

Parameters

[in] w Source bit pattern.

Returns: Float with the supplied encoding.

See implementation.

Return values

k_ra8_ok Operation succeeded.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 191 of file ra8_touch_cal.c.

References memcpy().

Referenced by ra8_touch_cal_load().

◆ internal_unpack_le32()

uint32_t internal_unpack_le32 ( const uint8_t * src )

static

Unpack a 32-bit little-endian word from a byte buffer.

Parameters

[in] src Source (4 bytes available).

Returns: Unpacked word.

See implementation.

Return values

k_ra8_ok Operation succeeded.

Precondition: Module state is consistent.; Module state is consistent.

Postcondition: Caller-visible state matches the documented contract.; Caller-visible state matches the documented contract.

Note: Not thread-safe unless documented otherwise.

Since: 0.1.0

Definition at line 142 of file ra8_touch_cal.c.

References k_internal_byte_shift_16, k_internal_byte_shift_24, and k_internal_byte_shift_8.

Referenced by ra8_touch_cal_load().

◆ ra8_touch_cal_apply()

ra8_err_t ra8_touch_cal_apply	(	ra8_touch_cal_point_t	raw,
		const ra8_touch_cal_matrix_t *	matrix,
		uint16_t	screen_width,
		uint16_t	screen_height,
		ra8_touch_cal_point_t *	out_screen )

nodiscard

Apply a calibration matrix to a single raw touch sample.

Computes (u, v) = M * (x, y) + t and clips to [0, screen_width-1] x [0, screen_height-1]. The clip is necessary because least-squares fits can map slightly off-panel raw samples to negative or beyond-panel pixel coordinates.

Parameters

[in]	raw	Raw controller sample.
[in]	matrix	Pre-computed affine transform.
[in]	screen_width	Panel width in pixels (>0).
[in]	screen_height	Panel height in pixels (>0).
[out]	out_screen	Destination screen pixel.

Returns: ra8_err_t error code.

Return values

k_ra8_ok	Sample mapped.
k_ra8_err_null_ptr	matrix or out_screen NULL.
k_ra8_err_invalid_arg	Panel size is zero.

Precondition: matrix, out_screen non-NULL.

Postcondition: out_screen->x in [0, screen_width-1].; out_screen->y in [0, screen_height-1].

Note: Pure function. Constant-time, branch-free except for the clip.

Since: 0.1.0

Definition at line 506 of file ra8_touch_cal.c.

References ra8_touch_cal_matrix_t::a, ra8_touch_cal_matrix_t::b, ra8_touch_cal_matrix_t::c, ra8_touch_cal_matrix_t::d, ra8_touch_cal_matrix_t::e, ra8_touch_cal_matrix_t::f, internal_clip32(), k_ra8_err_invalid_arg, k_ra8_err_null_ptr, k_ra8_ok, s_round_bias, ra8_touch_cal_point_t::x, and ra8_touch_cal_point_t::y.

Referenced by internal_tc_apply_and_measure().

◆ ra8_touch_cal_compute()

ra8_err_t ra8_touch_cal_compute	(	const ra8_touch_cal_point_t *	raw,
		const ra8_touch_cal_point_t *	screen,
		uint8_t	n,
		ra8_touch_cal_matrix_t *	out_mtx )

nodiscard

Compute an affine transform from N target/sample pairs.

Pure-math entry point. Solves the 3x3 normal-equation system per axis using Cramer's rule. The function does not touch any hardware and is the workhorse exercised by the unit tests.

Algorithm (Fang & Chang, eqn. 4–7):

Accumulate sums Sx, Sy, Sxx, Syy, Sxy, Sxu, Syu, Su, Sxv, Syv, Sv.
Compute det of the 3x3 system. Reject as k_ra8_err_invalid_arg if |det| is below ::k_ra8_touch_cal_min_det (panel-collinear targets).
Solve for (a, b, c) and (d, e, f) via Cramer's rule.

Parameters

[in]	raw	Array of n raw controller samples.
[in]	screen	Array of n corresponding screen targets.
[in]	n	Number of pairs (3..5).
[out]	out_mtx	Destination matrix.

Returns: ra8_err_t error code.

Return values

k_ra8_ok	Matrix populated.
k_ra8_err_null_ptr	Any pointer NULL.
k_ra8_err_invalid_arg	n out of range or system is singular.

Precondition: raw, screen, out_mtx non-NULL.; n in [k_ra8_touch_cal_min_targets, k_ra8_touch_cal_max_targets].

Postcondition: On success out_mtx holds the affine transform.; On error out_mtx is unmodified.

Note: Pure function – no hardware access, safe from any context.

Example:: ra8_touch_cal_point_t raw[5] = { ... };

ra8_touch_cal_point_t scr[5] = { ... };

ra8_touch_cal_matrix_t m = {};

if (ra8_touch_cal_compute(raw, scr, 5, &m) == k_ra8_ok) { ... }

k_ra8_ok
@ k_ra8_ok
Success – operation completed with all postconditions satisfied.
Definition ra8_err.h:119

ra8_touch_cal_compute
ra8_err_t ra8_touch_cal_compute(const ra8_touch_cal_point_t *raw, const ra8_touch_cal_point_t *screen, uint8_t n, ra8_touch_cal_matrix_t *out_mtx)
Compute an affine transform from N target/sample pairs.
Definition ra8_touch_cal.c:395

ra8_touch_cal_matrix_t
2-D affine transform screen = [a b; d e] * raw + [c; f].
Definition ra8_touch_cal.h:175

ra8_touch_cal_point_t
One (x, y) integer coordinate pair.
Definition ra8_touch_cal.h:150

See also: ra8_touch_cal_run; ra8_touch_cal_apply

Since: 0.1.0

Definition at line 395 of file ra8_touch_cal.c.

Referenced by ra8_touch_cal_run().

◆ ra8_touch_cal_load()

ra8_err_t ra8_touch_cal_load	(	const uint8_t *	src,
		size_t	src_size,
		ra8_touch_cal_matrix_t *	out_matrix )

nodiscard

Deserialise a calibration matrix from a byte blob.

Parameters

[in]	src	Source buffer (non-NULL, >= blob size).
[in]	src_size	Bytes available in src.
[out]	out_matrix	Destination matrix.

Returns: ra8_err_t error code.

Return values

k_ra8_ok	Blob accepted, matrix populated.
k_ra8_err_null_ptr	Any pointer NULL.
k_ra8_err_invalid_size	src_size is too small.
k_ra8_err_invalid_arg	Magic, version, or reserved bytes wrong.
k_ra8_err_crc_mismatch	CRC trailer does not match payload.

Precondition: src, out_matrix non-NULL.; src_size >= k_ra8_touch_cal_blob_size.

Postcondition: On error out_matrix is unmodified.

Since: 0.1.0

Definition at line 576 of file ra8_touch_cal.c.

References ra8_touch_cal_matrix_t::a, ra8_touch_cal_matrix_t::b, ra8_touch_cal_matrix_t::c, ra8_touch_cal_matrix_t::d, ra8_touch_cal_matrix_t::e, ra8_touch_cal_matrix_t::f, internal_crc32(), internal_u32_to_float(), internal_unpack_le32(), k_coeff_a, k_coeff_b, k_coeff_c, k_coeff_d, k_coeff_e, k_coeff_f, k_ra8_err_crc_mismatch, k_ra8_err_invalid_arg, k_ra8_err_invalid_size, k_ra8_err_null_ptr, k_ra8_ok, k_ra8_touch_cal_blob_size, k_ra8_touch_cal_magic_b0, k_ra8_touch_cal_magic_b1, k_ra8_touch_cal_magic_b2, k_ra8_touch_cal_magic_b3, k_ra8_touch_cal_off_coeffs, k_ra8_touch_cal_off_crc32, k_ra8_touch_cal_off_magic, k_ra8_touch_cal_off_reserved, k_ra8_touch_cal_off_version, and k_ra8_touch_cal_storage_version.

Referenced by internal_tc_blob_roundtrip().

◆ ra8_touch_cal_run()

ra8_err_t ra8_touch_cal_run	(	const ra8_touch_cal_run_cfg_t *	cfg,
		ra8_touch_cal_matrix_t *	out_matrix )

nodiscard

Drive the on-screen calibration sequence and produce a matrix.

For each of the five built-in targets (4 corners inset by cfg->inset_px plus the panel centre), this function:

Calls cfg->draw_target to paint the cross-hair.
Calls cfg->read_raw to capture the user's touch.
Stores the sample.

Once all five samples are captured, it invokes ra8_touch_cal_compute and copies the result into out_matrix.

Parameters

[in]	cfg	Configuration (non-NULL).
[out]	out_matrix	Destination matrix (non-NULL).

Returns: ra8_err_t error code.

Return values

k_ra8_ok	Calibration matrix produced.
k_ra8_err_null_ptr	Any pointer or shim NULL.
k_ra8_err_invalid_arg	Panel size or inset implausible, or solve failed.
k_ra8_err_hw_error	A draw or read shim returned non-OK.

Precondition: cfg->draw_target, cfg->read_raw non-NULL.; cfg->inset_px * 2 < min(width, height).

Postcondition: On success *out_matrix is fully written.

Note: Blocks for the duration of all five touches. Caller must ensure any concurrent UI is paused.

See also: ra8_touch_cal_compute

Since: 0.1.0

Definition at line 450 of file ra8_touch_cal.c.

References ra8_touch_cal_run_cfg_t::draw_ctx, ra8_touch_cal_run_cfg_t::draw_target, ra8_touch_cal_run_cfg_t::inset_px, k_internal_centre_div, k_ra8_err_hw_error, k_ra8_err_invalid_arg, k_ra8_err_null_ptr, k_ra8_ok, k_ra8_touch_cal_n_targets, ra8_touch_cal_compute(), ra8_touch_cal_run_cfg_t::read_ctx, ra8_touch_cal_run_cfg_t::read_raw, ra8_touch_cal_run_cfg_t::screen_height, and ra8_touch_cal_run_cfg_t::screen_width.

Referenced by internal_tc_run_calibration().

◆ ra8_touch_cal_save()

ra8_err_t ra8_touch_cal_save	(	const ra8_touch_cal_matrix_t *	matrix,
		uint8_t *	dst,
		size_t	dst_size )

nodiscard

Serialise a calibration matrix to a fixed-size byte blob.

Writes k_ra8_touch_cal_blob_size bytes laid out as documented in the file header. The byte order of the IEEE-754 float words is little-endian to match the Cortex-M85 native order. The blob is intended for ra8_flash page storage but the function does not touch flash itself – the caller is responsible for the actual write.

Parameters

[in]	matrix	Matrix to serialise (non-NULL).
[out]	dst	Destination buffer (non-NULL).
[in]	dst_size	Capacity of dst in bytes.

Returns: ra8_err_t error code.

Return values

k_ra8_ok	Blob written.
k_ra8_err_null_ptr	Any pointer NULL.
k_ra8_err_invalid_size	dst_size < k_ra8_touch_cal_blob_size.

Precondition: dst_size >= k_ra8_touch_cal_blob_size.

Postcondition: On success the first k_ra8_touch_cal_blob_size bytes of dst form a valid blob.

Note: Round-trip stable with ra8_touch_cal_load on any platform that uses IEEE-754 binary32 floats (i.e. all Cortex-M85 builds and all glibc / musl hosts).

Since: 0.1.0

Definition at line 538 of file ra8_touch_cal.c.

References ra8_touch_cal_matrix_t::a, ra8_touch_cal_matrix_t::b, ra8_touch_cal_matrix_t::c, ra8_touch_cal_matrix_t::d, ra8_touch_cal_matrix_t::e, ra8_touch_cal_matrix_t::f, internal_crc32(), internal_float_to_u32(), internal_pack_le32(), k_ra8_err_invalid_size, k_ra8_err_null_ptr, k_ra8_ok, k_ra8_touch_cal_blob_size, k_ra8_touch_cal_magic_b0, k_ra8_touch_cal_magic_b1, k_ra8_touch_cal_magic_b2, k_ra8_touch_cal_magic_b3, k_ra8_touch_cal_off_coeffs, k_ra8_touch_cal_off_crc32, k_ra8_touch_cal_off_magic, k_ra8_touch_cal_off_reserved, k_ra8_touch_cal_off_version, and k_ra8_touch_cal_storage_version.

Referenced by internal_tc_blob_roundtrip().

Variable Documentation

◆ s_min_det

const float s_min_det = 1.0e-3F

static

Floor for |det| below which the normal equations are treated as singular.

1e-3 is chosen empirically for a 1024x600 panel: real-world raw-sample spreads produce |det| in the 1e8 .. 1e10 range, so 1e-3 only trips on truly collinear inputs.

Note: File-scope static; not thread-shared because it is read-only.

Definition at line 93 of file ra8_touch_cal.c.

Referenced by internal_solve3().

◆ s_round_bias

const float s_round_bias = 0.5F

static

Round-to-nearest bias for float->int conversion.

Definition at line 96 of file ra8_touch_cal.c.

Referenced by ra8_touch_cal_apply().

Data Structures

Enumerations

Functions

Variables

Detailed Description

Enumeration Type Documentation

◆ affine_coeff_idx_t

◆ internal_const_t

◆ mat3_idx_t

Function Documentation

◆ internal_accumulate_sums()

◆ internal_clip32()

◆ internal_crc32()

◆ internal_float_to_u32()

◆ internal_pack_le32()

◆ internal_solve3()

◆ internal_u32_to_float()

◆ internal_unpack_le32()

◆ ra8_touch_cal_apply()

◆ ra8_touch_cal_compute()

◆ ra8_touch_cal_load()

◆ ra8_touch_cal_run()

◆ ra8_touch_cal_save()

Variable Documentation

◆ s_min_det

◆ s_round_bias