Add README

As it blocks the mc from reaching a ready state for unknown reason(s)

build/final.elf.map

@@ -36,6 +36,7 @@ Discarded input sections
  .group         0x00000000        0xc build/main.o
  .group         0x00000000        0xc build/main.o
  .group         0x00000000        0xc build/main.o
+ .group         0x00000000        0xc build/main.o
  .text          0x00000000        0x0 build/main.o
  .data          0x00000000        0x0 build/main.o
  .bss           0x00000000        0x0 build/main.o
@@ -52,7 +53,7 @@ Discarded input sections
  .debug_macro   0x00000000       0x89 build/main.o
  .debug_macro   0x00000000      0x4cc build/main.o
  .debug_macro   0x00000000       0x22 build/main.o
- .debug_macro   0x00000000       0x34 build/main.o
+ .debug_macro   0x00000000       0x46 build/main.o
  .group         0x00000000        0xc build/startup.o
  .group         0x00000000        0xc build/startup.o
  .group         0x00000000        0xc build/startup.o
@@ -96,6 +97,40 @@ Discarded input sections
  .debug_macro   0x00000000       0x89 build/timer.o
  .debug_macro   0x00000000      0x4cc build/timer.o
  .debug_macro   0x00000000       0x22 build/timer.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .group         0x00000000        0xc build/usart.o
+ .text          0x00000000        0x0 build/usart.o
+ .data          0x00000000        0x0 build/usart.o
+ .bss           0x00000000        0x0 build/usart.o
+ .debug_macro   0x00000000       0x22 build/usart.o
+ .debug_macro   0x00000000       0x75 build/usart.o
+ .debug_macro   0x00000000       0x2a build/usart.o
+ .debug_macro   0x00000000       0x5c build/usart.o
+ .debug_macro   0x00000000       0x3c build/usart.o
+ .debug_macro   0x00000000      0x103 build/usart.o
+ .debug_macro   0x00000000       0x3a build/usart.o
+ .debug_macro   0x00000000       0x57 build/usart.o
+ .debug_macro   0x00000000       0x6a build/usart.o
+ .debug_macro   0x00000000      0x1df build/usart.o
+ .debug_macro   0x00000000       0x89 build/usart.o
+ .debug_macro   0x00000000      0x4cc build/usart.o
+ .debug_macro   0x00000000      0x167 build/usart.o
+ .debug_macro   0x00000000       0x22 build/usart.o
+ .debug_macro   0x00000000       0x5e build/usart.o
 
 Memory Configuration
 
@@ -112,6 +147,7 @@ LOAD build/gpio.o
 LOAD build/main.o
 LOAD build/startup.o
 LOAD build/timer.o
+LOAD build/usart.o
                 0x20020000                        stack_start = (ORIGIN (sram) + LENGTH (sram))
 
 .isr_vector     0x08000000      0x198
@@ -121,126 +157,144 @@ LOAD build/timer.o
                 0x08000000                interrupt_vector_table
                 0x08000198                        . = ALIGN (0x4)
 
-.text           0x08000198      0x358
+.text           0x08000198      0x520
                 0x08000198                        . = ALIGN (0x4)
  *(.text)
  *(.text.*)
  .text.gpio_set_mode
                 0x08000198       0x62 build/gpio.o
                 0x08000198                gpio_set_mode
+ .text.gpio_set_af
+                0x080001fa       0x98 build/gpio.o
+                0x080001fa                gpio_set_af
  .text.gpio_write
-                0x080001fa       0x4c build/gpio.o
-                0x080001fa                gpio_write
- *fill*         0x08000246        0x2 
+                0x08000292       0x4c build/gpio.o
+                0x08000292                gpio_write
+ *fill*         0x080002de        0x2 
  .text.system_clock_init
-                0x08000248      0x144 build/main.o
- .text.main     0x0800038c       0x88 build/main.o
-                0x0800038c                main
+                0x080002e0      0x11c build/main.o
+ .text.main     0x080003fc       0x9c build/main.o
+                0x080003fc                main
  .text.init_memory
-                0x08000414       0x64 build/startup.o
-                0x08000414                init_memory
- .text.reset    0x08000478       0x10 build/startup.o
-                0x08000478                reset
+                0x08000498       0x64 build/startup.o
+                0x08000498                init_memory
+ .text.reset    0x080004fc       0x10 build/startup.o
+                0x080004fc                reset
  .text.default_handler
-                0x08000488        0x8 build/startup.o
-                0x08000488                exti0
-                0x08000488                debug_monitor
-                0x08000488                rcc
-                0x08000488                x
-                0x08000488                sdio
-                0x08000488                usage_fault
-                0x08000488                tim1_up_tim10
-                0x08000488                usart1
-                0x08000488                i2c3_er
-                0x08000488                spi2
-                0x08000488                dma1_stream1
-                0x08000488                bus_fault
-                0x08000488                spi5
-                0x08000488                exti3
-                0x08000488                dma2_stream5
-                0x08000488                tim2
-                0x08000488                dma1_stream6
-                0x08000488                default_handler
-                0x08000488                i2c1_er
-                0x08000488                hard_fault
-                0x08000488                usart6
-                0x08000488                exti15_10
-                0x08000488                usart2
-                0x08000488                pend_sv
-                0x08000488                i2c1_ev
-                0x08000488                wwdg
-                0x08000488                adc
-                0x08000488                rtc_alarm
-                0x08000488                spi3
-                0x08000488                exti1
-                0x08000488                mem_manage
-                0x08000488                dma2_stream1
-                0x08000488                dma1_stream2
-                0x08000488                dma2_stream3
-                0x08000488                sv_call
-                0x08000488                tim3
-                0x08000488                otg_fs
-                0x08000488                dma1_stream5
-                0x08000488                dma2_stream6
-                0x08000488                flash
-                0x08000488                tamp_stamp
-                0x08000488                i2c3_ev
-                0x08000488                rtc_wkup
-                0x08000488                dma2_stream0
-                0x08000488                pvd
-                0x08000488                fpu
-                0x08000488                exti4
-                0x08000488                exti2
-                0x08000488                spi1
-                0x08000488                dma1_stream0
-                0x08000488                tim1_brk_tim9
-                0x08000488                i2c2_ev
-                0x08000488                otg_fs_wkup
-                0x08000488                spi4
-                0x08000488                dma2_stream2
-                0x08000488                tim1_cc
-                0x08000488                tim1_trg_com_tim11
-                0x08000488                exti9_5
-                0x08000488                dma1_stream3
-                0x08000488                dma2_stream4
-                0x08000488                i2c2_er
-                0x08000488                dma2_stream7
-                0x08000488                dma1_stream7
-                0x08000488                nmi
-                0x08000488                systick
-                0x08000488                tim4
-                0x08000488                tim5
-                0x08000488                dma1_stream4
+                0x0800050c        0x8 build/startup.o
+                0x0800050c                exti0
+                0x0800050c                debug_monitor
+                0x0800050c                rcc
+                0x0800050c                x
+                0x0800050c                sdio
+                0x0800050c                usage_fault
+                0x0800050c                tim1_up_tim10
+                0x0800050c                usart1
+                0x0800050c                i2c3_er
+                0x0800050c                spi2
+                0x0800050c                dma1_stream1
+                0x0800050c                bus_fault
+                0x0800050c                spi5
+                0x0800050c                exti3
+                0x0800050c                dma2_stream5
+                0x0800050c                tim2
+                0x0800050c                dma1_stream6
+                0x0800050c                default_handler
+                0x0800050c                i2c1_er
+                0x0800050c                hard_fault
+                0x0800050c                usart6
+                0x0800050c                exti15_10
+                0x0800050c                usart2
+                0x0800050c                pend_sv
+                0x0800050c                i2c1_ev
+                0x0800050c                wwdg
+                0x0800050c                adc
+                0x0800050c                rtc_alarm
+                0x0800050c                spi3
+                0x0800050c                exti1
+                0x0800050c                mem_manage
+                0x0800050c                dma2_stream1
+                0x0800050c                dma1_stream2
+                0x0800050c                dma2_stream3
+                0x0800050c                sv_call
+                0x0800050c                tim3
+                0x0800050c                otg_fs
+                0x0800050c                dma1_stream5
+                0x0800050c                dma2_stream6
+                0x0800050c                flash
+                0x0800050c                tamp_stamp
+                0x0800050c                i2c3_ev
+                0x0800050c                rtc_wkup
+                0x0800050c                dma2_stream0
+                0x0800050c                pvd
+                0x0800050c                fpu
+                0x0800050c                exti4
+                0x0800050c                exti2
+                0x0800050c                spi1
+                0x0800050c                dma1_stream0
+                0x0800050c                tim1_brk_tim9
+                0x0800050c                i2c2_ev
+                0x0800050c                otg_fs_wkup
+                0x0800050c                spi4
+                0x0800050c                dma2_stream2
+                0x0800050c                tim1_cc
+                0x0800050c                tim1_trg_com_tim11
+                0x0800050c                exti9_5
+                0x0800050c                dma1_stream3
+                0x0800050c                dma2_stream4
+                0x0800050c                i2c2_er
+                0x0800050c                dma2_stream7
+                0x0800050c                dma1_stream7
+                0x0800050c                nmi
+                0x0800050c                systick
+                0x0800050c                tim4
+                0x0800050c                tim5
+                0x0800050c                dma1_stream4
  .text.tim4_init
-                0x08000490       0x40 build/timer.o
-                0x08000490                tim4_init
+                0x08000514       0x40 build/timer.o
+                0x08000514                tim4_init
  .text.tim4_start
-                0x080004d0       0x20 build/timer.o
-                0x080004d0                tim4_start
+                0x08000554       0x20 build/timer.o
+                0x08000554                tim4_start
+ .text.usart2_init
+                0x08000574       0xb8 build/usart.o
+                0x08000574                usart2_init
+ .text.usart2_start
+                0x0800062c       0x20 build/usart.o
+                0x0800062c                usart2_start
+ .text.usart2_write_byte
+                0x0800064c       0x30 build/usart.o
+                0x0800064c                usart2_write_byte
+ .text.usart2_write
+                0x0800067c       0x2a build/usart.o
+                0x0800067c                usart2_write
  *(.rodata)
+ *fill*         0x080006a6        0x2 
+ .rodata        0x080006a8        0xf build/main.o
  *(.rodata.*)
-                0x080004f0                        . = ALIGN (0x4)
-                0x080004f0                        _data_addr = LOADADDR (.data)
+                0x080006b8                        . = ALIGN (0x4)
+ *fill*         0x080006b7        0x1 
+                0x080006b8                        _data_addr = LOADADDR (.data)
 
-.glue_7         0x080004f0        0x0
- .glue_7        0x080004f0        0x0 linker stubs
+.glue_7         0x080006b8        0x0
+ .glue_7        0x080006b8        0x0 linker stubs
 
-.glue_7t        0x080004f0        0x0
- .glue_7t       0x080004f0        0x0 linker stubs
+.glue_7t        0x080006b8        0x0
+ .glue_7t       0x080006b8        0x0 linker stubs
 
-.vfp11_veneer   0x080004f0        0x0
- .vfp11_veneer  0x080004f0        0x0 linker stubs
+.vfp11_veneer   0x080006b8        0x0
+ .vfp11_veneer  0x080006b8        0x0 linker stubs
 
-.v4_bx          0x080004f0        0x0
- .v4_bx         0x080004f0        0x0 linker stubs
+.v4_bx          0x080006b8        0x0
+ .v4_bx         0x080006b8        0x0 linker stubs
 
-.iplt           0x080004f0        0x0
- .iplt          0x080004f0        0x0 build/main.o
+.iplt           0x080006b8        0x0
+ .iplt          0x080006b8        0x0 build/main.o
 
-.rel.dyn        0x080004f0        0x0
- .rel.iplt      0x080004f0        0x0 build/main.o
+.rel.dyn        0x080006b8        0x0
+ .rel.iplt      0x080006b8        0x0 build/main.o
 
-.data           0x20000000        0x0 load address 0x080004f0
+.data           0x20000000        0x0 load address 0x080006b8
                 0x20000000                        . = ALIGN (0x4)
                 0x20000000                        _data_start = .
  *(.data)
@@ -248,10 +302,10 @@ LOAD build/timer.o
                 0x20000000                        . = ALIGN (0x4)
                 0x20000000                        _data_end = .
 
-.igot.plt       0x20000000        0x0 load address 0x080004f0
+.igot.plt       0x20000000        0x0 load address 0x080006b8
  .igot.plt      0x20000000        0x0 build/main.o
 
-.bss            0x20000000        0x0 load address 0x080004f0
+.bss            0x20000000        0x0 load address 0x080006b8
                 0x20000000                        . = ALIGN (0x4)
                 0x20000000                        _bss_start = .
  *(.bss)
@@ -261,40 +315,46 @@ LOAD build/timer.o
 OUTPUT(build/final.elf elf32-littlearm)
 LOAD linker stubs
 
-.debug_info     0x00000000      0xb25
- .debug_info    0x00000000      0x21a build/gpio.o
- .debug_info    0x0000021a      0x44e build/main.o
- .debug_info    0x00000668      0x188 build/startup.o
- .debug_info    0x000007f0      0x335 build/timer.o
+.debug_info     0x00000000      0xf1e
+ .debug_info    0x00000000      0x262 build/gpio.o
+ .debug_info    0x00000262      0x47e build/main.o
+ .debug_info    0x000006e0      0x188 build/startup.o
+ .debug_info    0x00000868      0x335 build/timer.o
+ .debug_info    0x00000b9d      0x381 build/usart.o
 
-.debug_abbrev   0x00000000      0x44b
- .debug_abbrev  0x00000000      0x12b build/gpio.o
- .debug_abbrev  0x0000012b      0x144 build/main.o
- .debug_abbrev  0x0000026f      0x127 build/startup.o
- .debug_abbrev  0x00000396       0xb5 build/timer.o
+.debug_abbrev   0x00000000      0x5ae
+ .debug_abbrev  0x00000000      0x11d build/gpio.o
+ .debug_abbrev  0x0000011d      0x14b build/main.o
+ .debug_abbrev  0x00000268      0x127 build/startup.o
+ .debug_abbrev  0x0000038f       0xb5 build/timer.o
+ .debug_abbrev  0x00000444      0x16a build/usart.o
 
-.debug_aranges  0x00000000       0xa8
+.debug_aranges  0x00000000       0xe8
  .debug_aranges
-                0x00000000       0x28 build/gpio.o
+                0x00000000       0x30 build/gpio.o
  .debug_aranges
-                0x00000028       0x28 build/main.o
+                0x00000030       0x28 build/main.o
  .debug_aranges
-                0x00000050       0x30 build/startup.o
+                0x00000058       0x30 build/startup.o
  .debug_aranges
-                0x00000080       0x28 build/timer.o
+                0x00000088       0x28 build/timer.o
+ .debug_aranges
+                0x000000b0       0x38 build/usart.o
 
 .debug_rnglists
-                0x00000000       0x6c
+                0x00000000       0x99
  .debug_rnglists
-                0x00000000       0x19 build/gpio.o
+                0x00000000       0x20 build/gpio.o
  .debug_rnglists
-                0x00000019       0x1b build/main.o
+                0x00000020       0x1b build/main.o
  .debug_rnglists
-                0x00000034       0x1f build/startup.o
+                0x0000003b       0x1f build/startup.o
  .debug_rnglists
-                0x00000053       0x19 build/timer.o
+                0x0000005a       0x19 build/timer.o
+ .debug_rnglists
+                0x00000073       0x26 build/usart.o
 
-.debug_macro    0x00000000     0x3ba0
+.debug_macro    0x00000000     0x4853
  .debug_macro   0x00000000      0xb56 build/gpio.o
  .debug_macro   0x00000b56       0x22 build/gpio.o
  .debug_macro   0x00000b78       0x75 build/gpio.o
@@ -309,33 +369,39 @@ LOAD linker stubs
  .debug_macro   0x0000108c       0x89 build/gpio.o
  .debug_macro   0x00001115      0x4cc build/gpio.o
  .debug_macro   0x000015e1       0x22 build/gpio.o
- .debug_macro   0x00001603       0x34 build/gpio.o
- .debug_macro   0x00001637      0xb80 build/main.o
- .debug_macro   0x000021b7      0x12a build/main.o
- .debug_macro   0x000022e1       0x46 build/main.o
- .debug_macro   0x00002327       0x2e build/main.o
- .debug_macro   0x00002355       0x22 build/main.o
- .debug_macro   0x00002377      0xb02 build/startup.o
- .debug_macro   0x00002e79       0x56 build/startup.o
- .debug_macro   0x00002ecf       0x51 build/startup.o
- .debug_macro   0x00002f20      0xb5c build/timer.o
- .debug_macro   0x00003a7c      0x124 build/timer.o
+ .debug_macro   0x00001603       0x46 build/gpio.o
+ .debug_macro   0x00001649      0xb89 build/main.o
+ .debug_macro   0x000021d2      0x16d build/main.o
+ .debug_macro   0x0000233f       0x46 build/main.o
+ .debug_macro   0x00002385       0x2e build/main.o
+ .debug_macro   0x000023b3       0x22 build/main.o
+ .debug_macro   0x000023d5       0x5e build/main.o
+ .debug_macro   0x00002433      0xb02 build/startup.o
+ .debug_macro   0x00002f35       0x56 build/startup.o
+ .debug_macro   0x00002f8b       0x51 build/startup.o
+ .debug_macro   0x00002fdc      0xb5c build/timer.o
+ .debug_macro   0x00003b38      0x167 build/timer.o
+ .debug_macro   0x00003c9f      0xb74 build/usart.o
+ .debug_macro   0x00004813       0x40 build/usart.o
 
-.debug_line     0x00000000      0x4b9
- .debug_line    0x00000000      0x116 build/gpio.o
- .debug_line    0x00000116      0x1da build/main.o
- .debug_line    0x000002f0       0xea build/startup.o
- .debug_line    0x000003da       0xdf build/timer.o
+.debug_line     0x00000000      0x691
+ .debug_line    0x00000000      0x179 build/gpio.o
+ .debug_line    0x00000179      0x1d2 build/main.o
+ .debug_line    0x0000034b       0xea build/startup.o
+ .debug_line    0x00000435       0xdf build/timer.o
+ .debug_line    0x00000514      0x17d build/usart.o
 
-.debug_str      0x00000000     0x5eb8
- .debug_str     0x00000000     0x5372 build/gpio.o
-                               0x551a (size before relaxing)
- .debug_str     0x00005372      0xab2 build/main.o
-                               0x5f7c (size before relaxing)
- .debug_str     0x00005e24       0x88 build/startup.o
-                               0x3cdf (size before relaxing)
- .debug_str     0x00005eac        0xc build/timer.o
-                               0x5b1a (size before relaxing)
+.debug_str      0x00000000     0x626f
+ .debug_str     0x00000000     0x53d8 build/gpio.o
+                               0x5588 (size before relaxing)
+ .debug_str     0x000053d8      0xdce build/main.o
+                               0x62e8 (size before relaxing)
+ .debug_str     0x000061a6       0x88 build/startup.o
+                               0x3cdc (size before relaxing)
+ .debug_str     0x0000622e        0xc build/timer.o
+                               0x5c41 (size before relaxing)
+ .debug_str     0x0000623a       0x35 build/usart.o
+                               0x5fac (size before relaxing)
 
 .comment        0x00000000       0x45
  .comment       0x00000000       0x45 build/gpio.o
@@ -343,6 +409,7 @@ LOAD linker stubs
  .comment       0x00000045       0x46 build/main.o
  .comment       0x00000045       0x46 build/startup.o
  .comment       0x00000045       0x46 build/timer.o
+ .comment       0x00000045       0x46 build/usart.o
 
 .ARM.attributes
                 0x00000000       0x34
@@ -354,24 +421,30 @@ LOAD linker stubs
                 0x00000068       0x34 build/startup.o
  .ARM.attributes
                 0x0000009c       0x34 build/timer.o
+ .ARM.attributes
+                0x000000d0       0x34 build/usart.o
 
 .debug_line_str
-                0x00000000      0x283
+                0x00000000      0x290
  .debug_line_str
-                0x00000000      0x24e build/gpio.o
-                                0x260 (size before relaxing)
+                0x00000000      0x24b build/gpio.o
+                                0x25d (size before relaxing)
  .debug_line_str
-                0x0000024e       0x23 build/main.o
-                                0x27c (size before relaxing)
+                0x0000024b       0x2b build/main.o
+                                0x281 (size before relaxing)
  .debug_line_str
-                0x00000271        0xa build/startup.o
-                                0x21b (size before relaxing)
+                0x00000276        0xa build/startup.o
+                                0x218 (size before relaxing)
  .debug_line_str
-                0x0000027b        0x8 build/timer.o
-                                0x25e (size before relaxing)
+                0x00000280        0x8 build/timer.o
+                                0x25b (size before relaxing)
+ .debug_line_str
+                0x00000288        0x8 build/usart.o
+                                0x26c (size before relaxing)
 
-.debug_frame    0x00000000      0x16c
- .debug_frame   0x00000000       0x60 build/gpio.o
- .debug_frame   0x00000060       0x50 build/main.o
- .debug_frame   0x000000b0       0x6c build/startup.o
- .debug_frame   0x0000011c       0x50 build/timer.o
+.debug_frame    0x00000000      0x234
+ .debug_frame   0x00000000       0x88 build/gpio.o
+ .debug_frame   0x00000088       0x50 build/main.o
+ .debug_frame   0x000000d8       0x6c build/startup.o
+ .debug_frame   0x00000144       0x50 build/timer.o
+ .debug_frame   0x00000194       0xa0 build/usart.o

build/gpio.i

@@ -1,5 +1,5 @@
 # 0 "src/gpio.c"
-# 1 "/home/alex/code/own/c-compile-experiments//"
+# 1 "/home/alex/code/own/stm32-falling-sand//"
 # 0 "<built-in>"
 #define __STDC__ 1
 # 0 "<built-in>"
@@ -1995,17 +1995,23 @@ struct gpio {
   volatile uint32_t ODR;
   volatile uint32_t BSRR;
   volatile uint32_t LCKR;
-  volatile uint32_t AFRL[2];
-  volatile uint32_t AFRH[2];
+  volatile uint32_t AFRL;
+  volatile uint32_t AFRH;
 };
 
+
+#define GPIO_AF_MCO_1 (0b0000)
+#define GPIO_AF_USART2_RX (0b0111)
+#define GPIO_AF_USART2_TX (0b0111)
+
 #define GPIO_BASE_ADDR (0x40020000U)
 #define GPIO_PORT_OFFSET (0x400U)
 #define GPIO(port) ((struct gpio*)(uintptr_t)(GPIO_BASE_ADDR + (GPIO_PORT_OFFSET * port)))
 
-#define BIT(x) (1 << x)
 
-#define PIN(port,num) ((((port) - 'A') << 8) | num)
+#define PORT(port) (((port) - 'A') << 8)
+
+#define PIN(port,num) (PORT(port) | num)
 
 #define PINNUM(pin) (pin & 0b1111)
 
@@ -2019,24 +2025,37 @@ typedef enum {
 } GPIO_MODE;
 
 void gpio_set_mode(uint16_t pin, GPIO_MODE mode);
+void gpio_set_af(uint16_t pin, uint8_t af);
 void gpio_write(uint16_t pin, 
-# 40 "src/gpio.h" 3 4
+# 47 "src/gpio.h" 3 4
                              _Bool 
-# 40 "src/gpio.h"
+# 47 "src/gpio.h"
                                   val);
 # 5 "src/gpio.c" 2
 
 void gpio_set_mode(uint16_t pin, GPIO_MODE mode) {
   struct gpio *gpio = ((struct gpio*)(uintptr_t)((0x40020000U) + ((0x400U) * (pin >> 8))));
   int pn = (pin & 0b1111);
-  gpio->MODER &= ~(0x0011 << (pn * 2));
-  gpio->MODER |= (mode & 0b011) << (pn * 2);
+  gpio->MODER &= ~(0b11 << (pn * 2));
+  gpio->MODER |= (mode & 0b11) << (pn * 2);
+}
+
+void gpio_set_af(uint16_t pin, uint8_t af) {
+  struct gpio *gpio = ((struct gpio*)(uintptr_t)((0x40020000U) + ((0x400U) * (pin >> 8))));
+  int pn = (pin & 0b1111);
+  if (pn < 8) {
+ gpio->AFRL &= ~(0b1111 << (pn * 4));
+ gpio->AFRL |= (af & 0b1111) << (pn * 4);
+  } else {
+ gpio->AFRH &= ~(0b1111 << (pn * 4));
+ gpio->AFRH |= (af & 0b1111) << (pn * 4);
+  }
 }
 
 void gpio_write(uint16_t pin, 
-# 13 "src/gpio.c" 3 4
+# 25 "src/gpio.c" 3 4
                              _Bool 
-# 13 "src/gpio.c"
+# 25 "src/gpio.c"
                                   val) {
   struct gpio *gpio = ((struct gpio*)(uintptr_t)((0x40020000U) + ((0x400U) * (pin >> 8))));
   gpio->BSRR = (0b0011 << (pin & 0b1111)) << (val ? 0 : 16);

build/main.i

@@ -1,5 +1,5 @@
 # 0 "src/main.c"
-# 1 "/home/alex/code/own/c-compile-experiments//"
+# 1 "/home/alex/code/own/stm32-falling-sand//"
 # 0 "<built-in>"
 #define __STDC__ 1
 # 0 "<built-in>"
@@ -2070,6 +2070,19 @@ struct rcc {
 #define RCC_CFGR_PPRE_DIV_2 (0b100)
 
 
+#define RCC_CFGR_MCO1_HSE (0b10)
+#define RCC_CFGR_MCO1_PLL (0b11)
+
+#define RCC_CFGR_MCO1_BIT 21
+#define RCC_CFGR_MCO1_MASK (0b11)
+
+#define RCC_CFGR_MCO1PRE_DIV4 (0b110)
+#define RCC_CFGR_MCO1PRE_DIV2 (0b100)
+
+#define RCC_CFGR_MCO1PRE_BIT 24
+#define RCC_CFGR_MCO1PRE_MASK (0b111)
+
+
 #define RCC_CFGR_PPRE2_BIT 13
 #define RCC_CFGR_PPRE2_MASK (0b111)
 
@@ -2100,6 +2113,9 @@ struct rcc {
 #define RCC_APB1ENR_PWREN_BIT 28
 #define RCC_APB1ENR_PWREN_CLOCK_ENABLE (1 << RCC_APB1ENR_PWREN_BIT)
 
+#define RCC_APB1ENR_USART2EN_BIT 17
+#define RCC_APB1ENR_USART2EN_ENABLE (1 << RCC_APB1ENR_USART2EN_BIT)
+
 #define RCC_APB1ENR_TIM4_BIT 2
 #define RCC_APB1ENR_TIM4_ENABLE (1 << RCC_APB1ENR_TIM4_BIT)
 # 5 "src/main.c" 2
@@ -2119,17 +2135,23 @@ struct gpio {
   volatile uint32_t ODR;
   volatile uint32_t BSRR;
   volatile uint32_t LCKR;
-  volatile uint32_t AFRL[2];
-  volatile uint32_t AFRH[2];
+  volatile uint32_t AFRL;
+  volatile uint32_t AFRH;
 };
 
+
+#define GPIO_AF_MCO_1 (0b0000)
+#define GPIO_AF_USART2_RX (0b0111)
+#define GPIO_AF_USART2_TX (0b0111)
+
 #define GPIO_BASE_ADDR (0x40020000U)
 #define GPIO_PORT_OFFSET (0x400U)
 #define GPIO(port) ((struct gpio*)(uintptr_t)(GPIO_BASE_ADDR + (GPIO_PORT_OFFSET * port)))
 
-#define BIT(x) (1 << x)
 
-#define PIN(port,num) ((((port) - 'A') << 8) | num)
+#define PORT(port) (((port) - 'A') << 8)
+
+#define PIN(port,num) (PORT(port) | num)
 
 #define PINNUM(pin) (pin & 0b1111)
 
@@ -2143,10 +2165,11 @@ typedef enum {
 } GPIO_MODE;
 
 void gpio_set_mode(uint16_t pin, GPIO_MODE mode);
+void gpio_set_af(uint16_t pin, uint8_t af);
 void gpio_write(uint16_t pin, 
-# 40 "src/gpio.h" 3 4
+# 47 "src/gpio.h" 3 4
                              _Bool 
-# 40 "src/gpio.h"
+# 47 "src/gpio.h"
                                   val);
 # 6 "src/main.c" 2
 # 1 "src/flash.h" 1
@@ -2177,7 +2200,7 @@ struct flash {
 #define FLASH_ACR_ICEN_ENABLE (1 <<FLASH_ACR_ICEN_BIT)
 
 
-#define FLASH_ACR_LATENCY_3_WAIT_STATES (0x0111)
+#define FLASH_ACR_LATENCY_3_WAIT_STATES (0b0011)
 
 #define FLASH_ACR_LATENCY_BIT 0
 #define FLASH_ACR_LATENCY_MASK (0b1111)
@@ -2237,12 +2260,62 @@ struct timer {
 #define TIM4_BASE_ADDR (0x40000800U)
 #define TIM4 ((struct timer *) TIM4_BASE_ADDR)
 
-#define TIM4_CR_CEN_BIT 0
-#define TIM4_ENABLE (1 << TIM4_CR_CEN_BIT)
+#define TIM_CR1_CEN_BIT 0
+#define TIM_ENABLE (1 << TIM_CR1_CEN_BIT)
 
 void tim4_init(void);
 void tim4_start(void);
 # 9 "src/main.c" 2
+# 1 "src/usart.h" 1
+
+#define USART_H_ 
+
+
+
+struct usart {
+  volatile uint32_t SR;
+  volatile uint32_t DR;
+  volatile uint32_t BRR;
+  volatile uint32_t CR1;
+  volatile uint32_t CR2;
+  volatile uint32_t CR3;
+  volatile uint32_t GTPR;
+};
+
+#define USART2_BASE_ADDR (0x40004400U)
+#define USART2 ((struct usart *) USART2_BASE_ADDR)
+
+
+
+#define USART_SR_TC_BIT 6
+#define USART_SR_TC_COMPLETED (1 << USART_SR_TC_BIT)
+
+
+
+#define USART_CR1_UE_BIT 13
+#define USART_CR1_UE_ENABLE (1 << USART_CR1_UE_BIT)
+
+
+#define USART_CR1_TE_BIT 3
+#define USART_CR1_TE_ENABLE (1 << USART_CR1_TE_BIT)
+
+
+#define USART_CR1_RE_BIT 2
+#define USART_CR1_RE_ENABLE (1 << USART_CR1_RE_BIT)
+
+
+#define USART_BRR_MANTISSA_BIT 4
+#define USART_BRR_MANTISSA_MASK (0b111111111111)
+
+#define USART_BRR_FRACTION_BIT 0
+#define USART_BRR_FRACTION_MASK (0b111)
+
+void usart2_init(void);
+void usart2_start(void);
+
+void usart2_write_byte(uint8_t byte);
+void usart2_write(char *buf);
+# 10 "src/main.c" 2
 
 #define exit 42
 
@@ -2255,6 +2328,9 @@ static void system_clock_init(void) {
   ((struct pwr *) (0x40007000U))->CR |= ((0b11) << 14);
 
 
+  ((struct rcc *) (0x40023800U))->CR &= ~(1 << 0);
+
+
   ((struct rcc *) (0x40023800U))->CR |= (1 << 16);
 
 
@@ -2269,7 +2345,7 @@ static void system_clock_init(void) {
   ((struct rcc *) (0x40023800U))->PLLCFGR |= (1 << 22);
 
 
-  ((struct rcc *) (0x40023800U))->PLLCFGR |= ((25 & (0b111111)) << 0) | ((196 & (0b111111111)) << 6) | ((2 & (0b11)) << 16) | ((4 & (0b1111)) << 24);
+  ((struct rcc *) (0x40023800U))->PLLCFGR |= ((25 & (0b111111)) << 0) | ((192 & (0b111111111)) << 6) | ((2 & (0b11)) << 16) | ((4 & (0b1111)) << 24);
 
 
   ((struct rcc *) (0x40023800U))->CFGR &= ~((0b1111) << 4);
@@ -2288,33 +2364,32 @@ static void system_clock_init(void) {
 
 
 
-  while (!(((struct rcc *) (0x40023800U))->CR & (1 << 17)));
+  while (!(((struct rcc *) (0x40023800U))->CR & (1 << 25)));
 
 
   ((struct flash *) (0x40023C00U))->ACR |= (1 <<10);
   ((struct flash *) (0x40023C00U))->ACR |= (1 <<9);
 
 
-  ((struct flash *) (0x40023C00U))->ACR &= ~((0b1111) << 0);
-  ((struct rcc *) (0x40023800U))->CFGR |= ((0x0111) << 0);
 
 
-  ((struct rcc *) (0x40023800U))->CFGR &= ~((0b11) << 0);
-  ((struct rcc *) (0x40023800U))->CFGR |= ((0b10) << 0);
+
+
+
+  ((struct rcc *) (0x40023800U))->CFGR |= (((0b10) & (0b11)) << 0);
 
 
 
   while (((((struct rcc *) (0x40023800U))->CFGR >> 2) & (0b11)) != (0b10));
-
-
-  ((struct rcc *) (0x40023800U))->CR &= ~(1 << 0);
 }
 
 int main(void) {
   (void) system_clock_init();
   (void) tim4_init();
+  (void) usart2_init();
 
   (void) tim4_start();
+  (void) usart2_start();
 
   uint16_t led = (((('C') - 'A') << 8) | 13);
   ((struct rcc *) (0x40023800U))->AHB1ENR |= (1 << (led >> 8));
@@ -2322,19 +2397,21 @@ int main(void) {
 
   uint16_t counter = ((struct timer *) (0x40000800U))->CNT;
   
-# 87 "src/main.c" 3 4
+# 90 "src/main.c" 3 4
  _Bool 
-# 87 "src/main.c"
+# 90 "src/main.c"
       led_on = 
-# 87 "src/main.c" 3 4
+# 90 "src/main.c" 3 4
                ((_Bool)+0u)
-# 87 "src/main.c"
+# 90 "src/main.c"
                     ;
   while(1) {
  if ((((struct timer *) (0x40000800U))->CNT - counter) >= 250) {
   led_on = !led_on;
   gpio_write(led, led_on);
 
+  usart2_write("hello, world!\n");
+
   counter = ((struct timer *) (0x40000800U))->CNT;
  }
   };

build/startup.S

@@ -2923,6 +2923,8 @@ interrupt_vector_table:
 	.ascii	"INOR__ >= ((maj) << 16) + (min))\000"
 .LASF171:
 	.ascii	"__DBL_MAX__ ((double)1.7976931348623157e+308L)\000"
+.LASF602:
+	.ascii	"UINTMAX_C(x) __UINTMAX_C(x)\000"
 .LASF253:
 	.ascii	"__USFRACT_MIN__ 0.0UHR\000"
 .LASF578:
@@ -3020,8 +3022,8 @@ interrupt_vector_table:
 	.ascii	"__BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__\000"
 .LASF200:
 	.ascii	"__FLT32_MIN_10_EXP__ (-37)\000"
-.LASF176:
-	.ascii	"__DBL_HAS_DENORM__ 1\000"
+.LASF492:
+	.ascii	"__int20\000"
 .LASF267:
 	.ascii	"__LFRACT_IBIT__ 0\000"
 .LASF497:
@@ -3106,8 +3108,8 @@ interrupt_vector_table:
 	.ascii	"__ARM_NEON\000"
 .LASF401:
 	.ascii	"__ARM_FEATURE_CMSE\000"
-.LASF625:
-	.ascii	"/home/alex/code/own/c-compile-experiments\000"
+.LASF68:
+	.ascii	"__UINTPTR_TYPE__ unsigned int\000"
 .LASF229:
 	.ascii	"__FLT64_IS_IEC_60559__ 2\000"
 .LASF209:
@@ -3473,8 +3475,6 @@ interrupt_vector_table:
 	.ascii	"UINT16_C(x) __UINT16_C(x)\000"
 .LASF344:
 	.ascii	"__UTQ_FBIT__ 128\000"
-.LASF499:
-	.ascii	"__int20 +2\000"
 .LASF610:
 	.ascii	"long long int\000"
 .LASF24:
@@ -3539,8 +3539,8 @@ interrupt_vector_table:
 	.ascii	"__STDC__ 1\000"
 .LASF17:
 	.ascii	"__SIZEOF_LONG__ 4\000"
-.LASF492:
-	.ascii	"__int20\000"
+.LASF499:
+	.ascii	"__int20 +2\000"
 .LASF168:
 	.ascii	"__DBL_MAX_EXP__ 1024\000"
 .LASF585:
@@ -3567,6 +3567,8 @@ interrupt_vector_table:
 	.ascii	"__SCHAR_WIDTH__ 8\000"
 .LASF298:
 	.ascii	"__ACCUM_MIN__ (-0X1P15K-0X1P15K)\000"
+.LASF40:
+	.ascii	"__CHAR16_TYPE__ short unsigned int\000"
 .LASF21:
 	.ascii	"__SIZEOF_DOUBLE__ 8\000"
 .LASF7:
@@ -3801,8 +3803,8 @@ interrupt_vector_table:
 	.ascii	"SIZE_MAX (__SIZE_MAX__)\000"
 .LASF54:
 	.ascii	"__INT_LEAST64_TYPE__ long long int\000"
-.LASF602:
-	.ascii	"UINTMAX_C(x) __UINTMAX_C(x)\000"
+.LASF128:
+	.ascii	"__INT_FAST16_MAX__ 0x7fffffff\000"
 .LASF49:
 	.ascii	"__UINT32_TYPE__ long unsigned int\000"
 .LASF183:
@@ -3879,8 +3881,8 @@ interrupt_vector_table:
 	.ascii	"INT64_MAX (__INT64_MAX__)\000"
 .LASF518:
 	.ascii	"_INT8_T_DECLARED \000"
-.LASF40:
-	.ascii	"__CHAR16_TYPE__ short unsigned int\000"
+.LASF625:
+	.ascii	"/home/alex/code/own/stm32-falling-sand\000"
 .LASF370:
 	.ascii	"__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1\000"
 .LASF151:
@@ -4044,8 +4046,8 @@ interrupt_vector_table:
 	.ascii	"__FLT32X_MAX_10_EXP__ 308\000"
 .LASF140:
 	.ascii	"__UINTPTR_MAX__ 0xffffffffU\000"
-.LASF128:
-	.ascii	"__INT_FAST16_MAX__ 0x7fffffff\000"
+.LASF176:
+	.ascii	"__DBL_HAS_DENORM__ 1\000"
 .LASF32:
 	.ascii	"__GNUC_EXECUTION_CHARSET_NAME \"UTF-8\"\000"
 .LASF475:
@@ -4072,8 +4074,6 @@ interrupt_vector_table:
 	.ascii	"long +4\000"
 .LASF534:
 	.ascii	"__int_least8_t_defined 1\000"
-.LASF68:
-	.ascii	"__UINTPTR_TYPE__ unsigned int\000"
 .LASF92:
 	.ascii	"__UINTMAX_MAX__ 0xffffffffffffffffULL\000"
 .LASF42:

build/startup.i

@@ -1,5 +1,5 @@
 # 0 "src/startup.c"
-# 1 "/home/alex/code/own/c-compile-experiments//"
+# 1 "/home/alex/code/own/stm32-falling-sand//"
 # 0 "<built-in>"
 #define __STDC__ 1
 # 0 "<built-in>"

build/timer.i

@@ -1,5 +1,5 @@
 # 0 "src/timer.c"
-# 1 "/home/alex/code/own/c-compile-experiments//"
+# 1 "/home/alex/code/own/stm32-falling-sand//"
 # 0 "<built-in>"
 #define __STDC__ 1
 # 0 "<built-in>"
@@ -2055,6 +2055,19 @@ struct rcc {
 #define RCC_CFGR_PPRE_DIV_2 (0b100)
 
 
+#define RCC_CFGR_MCO1_HSE (0b10)
+#define RCC_CFGR_MCO1_PLL (0b11)
+
+#define RCC_CFGR_MCO1_BIT 21
+#define RCC_CFGR_MCO1_MASK (0b11)
+
+#define RCC_CFGR_MCO1PRE_DIV4 (0b110)
+#define RCC_CFGR_MCO1PRE_DIV2 (0b100)
+
+#define RCC_CFGR_MCO1PRE_BIT 24
+#define RCC_CFGR_MCO1PRE_MASK (0b111)
+
+
 #define RCC_CFGR_PPRE2_BIT 13
 #define RCC_CFGR_PPRE2_MASK (0b111)
 
@@ -2085,6 +2098,9 @@ struct rcc {
 #define RCC_APB1ENR_PWREN_BIT 28
 #define RCC_APB1ENR_PWREN_CLOCK_ENABLE (1 << RCC_APB1ENR_PWREN_BIT)
 
+#define RCC_APB1ENR_USART2EN_BIT 17
+#define RCC_APB1ENR_USART2EN_ENABLE (1 << RCC_APB1ENR_USART2EN_BIT)
+
 #define RCC_APB1ENR_TIM4_BIT 2
 #define RCC_APB1ENR_TIM4_ENABLE (1 << RCC_APB1ENR_TIM4_BIT)
 # 2 "src/timer.c" 2
@@ -2120,8 +2136,8 @@ struct timer {
 #define TIM4_BASE_ADDR (0x40000800U)
 #define TIM4 ((struct timer *) TIM4_BASE_ADDR)
 
-#define TIM4_CR_CEN_BIT 0
-#define TIM4_ENABLE (1 << TIM4_CR_CEN_BIT)
+#define TIM_CR1_CEN_BIT 0
+#define TIM_ENABLE (1 << TIM_CR1_CEN_BIT)
 
 void tim4_init(void);
 void tim4_start(void);
@@ -2137,7 +2153,7 @@ void tim4_init(void) {
 
 
 
-  ((struct timer *) (0x40000800U))->PSC = (uint16_t) 48000 - 1;
+  ((struct timer *) (0x40000800U))->PSC = (uint16_t) 96000 - 1;
 
 
   ((struct timer *) (0x40000800U))->ARR = (uint16_t) 0xFFFF;