Pin #	Pin name	function	settings	comment
1	PE2	DIAG	in	`diag` output of TMC
2	PE3	MUL0	slow out	multiplexer address
3	PE4	MUL1	slow out	for DIAG input
4	PE5	MUL2	slow out
5	PE6	MUL EN	slow out	enable mul.
6	(vbat)	-	-
7	PC13	M0 L1	slow in PU/out	enable motor
8	PC14	M0 L0	slow in PU	direction of motor
9	PC15	M0 DIR	slow out	limit-switch 0
10	PF9	M0 STEP	AF	clock of motor
11	PF10	M0 EN	slow out	l-s 0 or CS of SPI
12	(OSC IN)
13	(OSC OUT)
14	(nrst)			reset
15	PC0	MOTMUL0	slow out	external motors
16	PC1	MOTMUL1	slow out	multiplexer
17	PC2	MOTMUL2	slow out
18	PC3	MOTMUL EN	slow out
19	PF2	ADC2 in10	ADC	5V in / 2
20	(VSSA)
21	(VREF+)
22	(VDDA)
23	PA0	ADC1 in1	ADC	External ADC inputs
24	PA1	ADC1 in2	ADC
25	PA2	ADC1 in3	ADC
26	PA3	ADC1 in4	ADC
27	(VSS)
28	(VDD)
29	PA4	ADC2 in1	ADC	Vdrive / 10
30	PA5	SPI1 SCK	AF	In case of SPI TMC
31	PA6	SPI1 MISO	AF
32	PA7	SPI1 MOSI	AF
33	PC4	USART1 Tx	AF	External USART
34	PC5	USART1 Rx	AF
35	PB0	M7 STEP	AF
36	PB1	M7 EN	slow out
37	PB2	M7 DIR	slow out
38	PE7	M7 L0	slow in PU
39	PE8	M7 L1	slow in PU/out
40	PE9	M6 STEP	AF
41	PE10	M6 L1	slow in PU/out
42	PE11	M6 L0	slow in PU
43	PE12	M6 DIR	slow out
44	PE13	M6 EN	slow out
45	PE14	OUT2	slow in PU/out	external GPIO
46	PE15	OUT1	slow in PU/out
47	PB10	USART3 Tx	AF	USART for 4 of TMC
48	PB11	OUT0	slow in PU/out
49	(VSS)
50	(VDD)
51	PB12	SCRN DCRS	slow out	screen commands
52	PB13	SCRN SCK	AF	SPI for screen
53	PB14	SCRN MISO	AF
54	PB15	SCRN MOSI	AF
55	PD8	SCRN RST	slow out	reset screen
56	PD9	SCRN CS	slow out	activate screen
57	PD10	M5 L1	slow in PU/out
58	PD11	M5 L0	slow in PU
59	PD12	M5 STEP	AF
60	PD13	M5 DIR	slow out
61	PD14	M5 EN	slow out
62	PD15	M4 L1	slow in PU/out
63	PC6	M4 STEP	AF
64	PC7	M4 L0	slow in PU
65	PC8	M4 DIR	slow out
66	PC9	M4 EN	slow out
67	PA8	USBpu	slow out PP	USB DP pullup
68	PA9	BTN1	slow in PU	buttons to operate
69	PA10	BTN2 (SDA)	slow in PU/AF	with screen
70	PA11	USB DM	AF	USB
71	PA12	USB DP	AF
72	PA13	SWDIO	dflt	dbg/flash
73	PF6	BTN3 (SCL)	slow in PU/AF	(possible I2C2)
74	(VSS)
75	(VDD)
76	PA14	SWCLK	dflt	debug/sew
77	PA15	M3 STEP	AF
78	PC10	M3 L0	slow in PU
79	PC11	M3 L1	slow in PU/out
80	PC12	M3 DIR	slow out
81	PD0	CAN Rx	AF	CAN bus
82	PD1	CAN Tx	AF
83	PD2	M3 EN	slow out
84	PD3	BTN4	slow in PU
85	PD4	BTN5	slow in PU
86	PD5	BTN6	slow in PU
87	PD6	M2 L1	slow in PU
88	PD7	M2 L0	slow in PU/out
89	PB3	USART2 Tx	AF	USART for 4 of TMC
90	PB4	M2 DIR	slow out
91	PB5	M2 STEP	AF
92	PB6	M2 EN	slow out
93	PB7	M1 L1	slow in PU/out
94	(BOOT0)			boot mode
95	PB8	M1 STEP	AF
96	PB9	M1 L0	slow in PU
97	PE0	M1 DIR	slow out
98	PE1	M1 EN	slow out
99	(VSS)
100	(VDD)

Some comments.

DIAG input used to detect problems with TMC drivers (multiplexed by MUL outputs). Each motor have next control signals: EN - enable driver, DIR - rotation direction, STEP - microstepping clock signal, L0 - zero end-switch, L1 - max end-switch (or Cable Select for SPI-based TMC). MOTMUL - external multiplexer or other GPIO signals (e.g. to manage of 64 stepper motors). ADC1 in - four external ADC signals (0..3.3V). SPI1 used to manage TMC drivers in case of SPI-based. USART1 - to connect external something (master or slave). OUT - external GPIO. USART2 Tx used to manage USART-based TMC (numbers 0-3). USART3 Tx used to manage USART-based TMC (numbers 4-7). SCRN - control signals for SPI TFT screen. BTN - external button, keypad, joystick etc. Two of them could be connected to I2C devices. USB and CAN used as main device control buses. SW used as debugging/sewing; also (I remember about USB pullup only after end of PCB design) SWDIO used as USB pullup (so the device have no USB in debug mode - when BTN0 and BTN1 are pressed at start).

Sorted by ports (with AF numbers).

Pin #	Pin name	function	settings	comment
23	PA0	ADC1 in1	ADC	External ADC inputs
24	PA1	ADC1 in2	ADC
25	PA2	ADC1 in3	ADC
26	PA3	ADC1 in4	ADC
29	PA4	ADC2 in1	ADC	Vdrive / 10
30	PA5	SPI1 SCK	AF5	In case of SPI TMC
31	PA6	SPI1 MISO	AF5
32	PA7	SPI1 MOSI	AF5
67	PA8	BTN0	slow in PU	Buttons/joystick
68	PA9	BTN1	slow in PU	to operate with
69	PA10	BTN2 (SDA)	slow in PU/AF4	screen
70	PA11	USB DM	USB	USB
71	PA12	USB DP	USB
72	PA13	SWDIO/USBpu	dflt/slow out	USB pullup or dbg
76	PA14	SWCLK	dflt	debug/sew
77	PA15	M3 STEP	AF1 (T2ch1)
35	PB0	M7 STEP	AF2 (T3ch3)
36	PB1	M7 EN	slow out
37	PB2	M7 DIR	slow out
89	PB3	USART2 Tx	AF7	USART for 4 of TMC
90	PB4	M2 DIR	slow out
91	PB5	M2 STEP	AF10 (T17ch1)
92	PB6	M2 EN	slow out
93	PB7	M1 L1	slow in PU/out
95	PB8	M1 STEP	AF1 (T16ch1)
96	PB9	M1 L0	slow in PU
47	PB10	USART3 Tx	AF7	USART for 4 of TMC
48	PB11	OUT0	slow in PU/out
51	PB12	SCRN DCRS	slow out	screen commands
52	PB13	SCRN SCK	AF5	SPI for screen
53	PB14	SCRN MISO	AF5
54	PB15	SCRN MOSI	AF5
15	PC0	MOTMUL0	slow out	external motors
16	PC1	MOTMUL1	slow out	multiplexer
17	PC2	MOTMUL2	slow out
18	PC3	MOTMUL EN	slow out
33	PC4	USART1 Tx	AF7	External USART
34	PC5	USART1 Rx	AF7
63	PC6	M4 STEP	AF4 (T8ch1)
64	PC7	M4 L0	slow in PU
65	PC8	M4 DIR	slow out
66	PC9	M4 EN	slow out
78	PC10	M3 L0	slow in PU
79	PC11	M3 L1	slow in PU/out
80	PC12	M3 DIR	slow out
7	PC13	M0 L1	slow in PU/out	enable motor
8	PC14	M0 L0	slow in PU	direction of motor
9	PC15	M0 DIR	slow out	limit-switch 0
81	PD0	CAN Rx	AF7	CAN bus
82	PD1	CAN Tx	AF7
83	PD2	M3 EN	slow out
84	PD3	BTN4	slow in PU
85	PD4	BTN5	slow in PU
86	PD5	BTN6	slow in PU
87	PD6	M2 L1	slow in PU
88	PD7	M2 L0	slow in PU/out
55	PD8	SCRN RST	slow out	reset screen
56	PD9	SCRN CS	slow out	activate screen
57	PD10	M5 L1	slow in PU/out
58	PD11	M5 L0	slow in PU
59	PD12	M5 STEP	AF2 (T4ch1)
60	PD13	M5 DIR	slow out
61	PD14	M5 EN	slow out
62	PD15	M4 L1	slow in PU/out
97	PE0	M1 DIR	slow out
98	PE1	M1 EN	slow out
1	PE2	DIAG	slow in PU	`diag` output of TMC
2	PE3	MUL0	slow out	multiplexer address
3	PE4	MUL1	slow out	for DIAG input
4	PE5	MUL2	slow out
5	PE6	MUL EN	slow out	enable mul.
38	PE7	M7 L0	slow in PU
39	PE8	M7 L1	slow in PU/out
40	PE9	M6 STEP	AF2 (T1ch1)
41	PE10	M6 L1	slow in PU/out
42	PE11	M6 L0	slow in PU
43	PE12	M6 DIR	slow out
44	PE13	M6 EN	slow out
45	PE14	OUT2	slow in PU/out	external GPIO
46	PE15	OUT1	slow in PU/out
19	PF2	ADC2 in10	ADC	5V in / 2
73	PF6	BTN3 (SCL)	slow in PU/AF4	(possible I2C2)
10	PF9	M0 STEP	AF3 (T15ch1)	clock of motor
11	PF10	M0 EN	slow out	l-s 0 or CS of SPI

DMA usage

ADC1 - DMA1_ch1
ADC2 - DMA2_ch1
USART2 (PDN-UART for drivers 0..3) - DMA1_ch6 (Rx), DMA1_ch7 (Tx)
USART3 (PDN-UART for drivers 4..7) - DMA1_ch3 (Rx), DMA1_ch2 (Tx)
SPI2 (screen) - DMA1_ch4 (Rx), DMA1_ch5 (Tx) [or may be dedicated to USART1]

Other stepper drivers connection

DRV8825

Solder jumpers E2, B and A to connect ~RST and ~SLP to 3.3V.

Microstepping selection produced by soldering H2 (bit0), G2 (bit1) and/or C (bit2).