spi-i2c-baremetal

Name: spi-i2c-baremetal
Author: mohitmishra786

141stars19forks

How to install spi-i2c-baremetal?

mohitmishra786/low-level-dev-skills/spi-i2c-baremetal

$npx -y skills add mohitmishra786/low-level-dev-skills --skill spi-i2c-baremetal

Installs into the current project.

Summary

Bare-metal SPI and I2C skill for serial peripheral buses. Use when implementing master-mode transfers, register read/write protocols, or debugging bus stalls. Activates on queries about SPI bare-metal, I2C START/STOP, sensor register read, or clock phase/polarity.

Files · 1

View on GitHub

SKILL.md

1	# SPI and I2C (Bare-Metal)
2
3	## Purpose
4
5	Implement SPI and I2C master drivers for sensor and memory chips: clock configuration, phase/polarity (SPI), START/ACK sequences (I2C), and common register-oriented transaction patterns.
6
7	## When to Use
8
9	- Reading an I2C sensor (WHO_AM_I register)
10	- SPI flash or display bring-up
11	- Debugging NACK or stuck SCL
12	- Replacing HAL_I2C/SPI with minimal code
13
14	## Workflow
15
16	### 1. SPI master (STM32)
17
18	```c
19	/* Mode 0: CPOL=0, CPHA=0 — check slave datasheet */
20	SPI1->CR1 = SPI_CR1_MSTR \| SPI_CR1_SSM \| SPI_CR1_SSI
21	\| (3 << SPI_CR1_BR_Pos); /* baud divider */
22	SPI1->CR1 \|= SPI_CR1_SPE;
23
24	uint8_t spi_xfer(SPI_TypeDef *spi, uint8_t tx) {
25	while (!(spi->SR & SPI_SR_TXE))
26	;
27	(volatile uint8_t )&spi->DR = tx;
28	while (!(spi->SR & SPI_SR_RXNE))
29	;
30	return (volatile uint8_t )&spi->DR;
31	}
32	```
33
34	CS (GPIO bit-bang):
35
36	```c
37	GPIO_CS_LOW();
38	spi_xfer(SPI1, reg \| 0x80); /* read */
39	uint8_t val = spi_xfer(SPI1, 0xFF);
40	GPIO_CS_HIGH();
41	```
42
43	### 2. I2C master — register read
44
45	```c
46	/* START → addr+W → reg → repeated START → addr+R → data → STOP */
47	bool i2c_read_reg(I2C_TypeDef i2c, uint8_t dev7, uint8_t reg, uint8_t out) {
48	if (!i2c_start(i2c)) return false;
49	if (!i2c_tx(i2c, (dev7 << 1) \| 0)) return false;
50	if (!i2c_tx(i2c, reg)) return false;
51	if (!i2c_restart(i2c)) return false;
52	if (!i2c_tx(i2c, (dev7 << 1) \| 1)) return false;
53	out = i2c_rx(i2c, false); / NACK last byte */
54	i2c_stop(i2c);
55	return true;
56	}
57	```
58
59	Poll `SB`, `ADDR`, `TXE`, `RXNE`, `BTF` per reference manual.
60
61	### 3. Common protocols
62
63	\| Pattern \| Bus \|
64	\|---------\|-----\|
65	\| `reg + write data` \| I2C/SPI \|
66	\| `0x80\|reg` read (MSB set) \| SPI sensors \|
67	\| 16-bit big-endian length prefix \| SPI flash \|
68
69	### 4. Agent usage
70
71	```
72	/spi-i2c-baremetal I2C read of register 0x0F from device 0x68
73	```
74
75	## Common Problems
76
77	\| Symptom \| Cause \| Fix \|
78	\|---------\|-------\|-----\|
79	\| I2C NACK \| Wrong 7-bit addr (8-bit in datasheet) \| Shift addr; check R/W bit \|
80	\| SPI garbage \| CPOL/CPHA mismatch \| Match slave mode table \|
81	\| Bus stuck SCL low \| Slave clock stretch / fault \| Bus recovery (clock pulses) \|
82	\| CS glitch \| CS timing vs clock \| Assert CS before first SCK \|
83
84	## Related Skills
85
86	- `skills/baremetal/gpio-baremetal` — CS, SDA, SCL pins
87	- `skills/baremetal/peripherals-from-datasheet` — timing requirements
88	- `skills/kernel-dev/bus-drivers-i2c-spi` — Linux kernel side

People who liked this also viewed

6 picks

Type

spi-i2c-baremetal

141stars19forks

View on GitHub

How to install spi-i2c-baremetal?

mohitmishra786/low-level-dev-skills/spi-i2c-baremetal

$npx -y skills add mohitmishra786/low-level-dev-skills --skill spi-i2c-baremetal

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# SPI and I2C (Bare-Metal)
2
3	## Purpose
4
5	Implement SPI and I2C master drivers for sensor and memory chips: clock configuration, phase/polarity (SPI), START/ACK sequences (I2C), and common register-oriented transaction patterns.
6
7	## When to Use
8
9	- Reading an I2C sensor (WHO_AM_I register)
10	- SPI flash or display bring-up
11	- Debugging NACK or stuck SCL
12	- Replacing HAL_I2C/SPI with minimal code
13
14	## Workflow
15
16	### 1. SPI master (STM32)
17
18	```c
19	/* Mode 0: CPOL=0, CPHA=0 — check slave datasheet */
20	SPI1->CR1 = SPI_CR1_MSTR \| SPI_CR1_SSM \| SPI_CR1_SSI
21	\| (3 << SPI_CR1_BR_Pos); /* baud divider */
22	SPI1->CR1 \|= SPI_CR1_SPE;
23
24	uint8_t spi_xfer(SPI_TypeDef *spi, uint8_t tx) {
25	while (!(spi->SR & SPI_SR_TXE))
26	;
27	(volatile uint8_t )&spi->DR = tx;
28	while (!(spi->SR & SPI_SR_RXNE))
29	;
30	return (volatile uint8_t )&spi->DR;
31	}
32	```
33
34	CS (GPIO bit-bang):
35
36	```c
37	GPIO_CS_LOW();
38	spi_xfer(SPI1, reg \| 0x80); /* read */
39	uint8_t val = spi_xfer(SPI1, 0xFF);
40	GPIO_CS_HIGH();
41	```
42
43	### 2. I2C master — register read
44
45	```c
46	/* START → addr+W → reg → repeated START → addr+R → data → STOP */
47	bool i2c_read_reg(I2C_TypeDef i2c, uint8_t dev7, uint8_t reg, uint8_t out) {
48	if (!i2c_start(i2c)) return false;
49	if (!i2c_tx(i2c, (dev7 << 1) \| 0)) return false;
50	if (!i2c_tx(i2c, reg)) return false;
51	if (!i2c_restart(i2c)) return false;
52	if (!i2c_tx(i2c, (dev7 << 1) \| 1)) return false;
53	out = i2c_rx(i2c, false); / NACK last byte */
54	i2c_stop(i2c);
55	return true;
56	}
57	```
58
59	Poll `SB`, `ADDR`, `TXE`, `RXNE`, `BTF` per reference manual.
60
61	### 3. Common protocols
62
63	\| Pattern \| Bus \|
64	\|---------\|-----\|
65	\| `reg + write data` \| I2C/SPI \|
66	\| `0x80\|reg` read (MSB set) \| SPI sensors \|
67	\| 16-bit big-endian length prefix \| SPI flash \|
68
69	### 4. Agent usage
70
71	```
72	/spi-i2c-baremetal I2C read of register 0x0F from device 0x68
73	```
74
75	## Common Problems
76
77	\| Symptom \| Cause \| Fix \|
78	\|---------\|-------\|-----\|
79	\| I2C NACK \| Wrong 7-bit addr (8-bit in datasheet) \| Shift addr; check R/W bit \|
80	\| SPI garbage \| CPOL/CPHA mismatch \| Match slave mode table \|
81	\| Bus stuck SCL low \| Slave clock stretch / fault \| Bus recovery (clock pulses) \|
82	\| CS glitch \| CS timing vs clock \| Assert CS before first SCK \|
83
84	## Related Skills
85
86	- `skills/baremetal/gpio-baremetal` — CS, SDA, SCL pins
87	- `skills/baremetal/peripherals-from-datasheet` — timing requirements
88	- `skills/kernel-dev/bus-drivers-i2c-spi` — Linux kernel side

People who liked this also viewed

6 picks

Type