finally got the uart working
This commit is contained in:
David Welch
30
uart01/Makefile
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30
uart01/Makefile
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ARMGNU ?= arm-none-eabi
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COPS = -Wall -O2 -nostdlib -nostartfiles -ffreestanding
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all : kernel.img
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clean :
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rm -f *.o
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rm -f *.bin
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rm -f *.elf
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rm -f *.list
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rm -f *.img
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novectors.o : novectors.s
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$(ARMGNU)-as novectors.s -o novectors.o
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uart01.o : uart01.c
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$(ARMGNU)-gcc $(COPS) -c uart01.c -o uart01.o
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kernel.img : memmap novectors.o uart01.o
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$(ARMGNU)-ld novectors.o uart01.o -T memmap -o uart01.elf
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$(ARMGNU)-objdump -D uart01.elf > uart01.list
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$(ARMGNU)-objcopy uart01.elf -O binary kernel.img
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25
uart01/README
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25
uart01/README
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See the top level README for information on where to find the
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schematic and programmers reference manual for the ARM processor
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on the raspberry pi.
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Okay this was incredibly painful. I might have saved a few hours if
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was at the office with an oscilloscope, I eventually had to fashion
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something to look at the output using an mbed.
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The documentation for the chip has some glaring errors. The IER and
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IIR register descriptions are screwy. The one that killed me was
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the word length. The document says that the single bit controls 7
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bits per word vs 8 bits per word. And that bit 1 and some above
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do not do anything, they might on real 16550's but not here. Well
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that is wrong. If bits 1:0 are 00 you get 7 bits if bits 1:0 are 01
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you get 7 bits. You need bit 1 set to get 8 bits.
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This example uses the mini uart, uart1, to transmit characters on
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GPIO14. You will need a level shifter or something that can receive
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3.3v. One like this http://www.sparkfun.com/products/718 works perfectly.
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Connect ground to pin 6 of P1 and rx on the FTDI board to tx on the
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raspi which is pin 8 on the P1 connector.
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This example sets up the uart for 115200 baud, and blasts the characters
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0123456701234567...forever as fast as it can.
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12
uart01/memmap
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12
uart01/memmap
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MEMORY
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{
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ram : ORIGIN = 0x00000000, LENGTH = 0x1000
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}
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SECTIONS
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{
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.text : { *(.text*) } > ram
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.bss : { *(.bss*) } > ram
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}
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23
uart01/novectors.s
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23
uart01/novectors.s
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.globl _start
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_start:
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b reset
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reset:
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mov sp,#0x1000
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bl notmain
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hang: b hang
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.globl PUT32
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PUT32:
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str r1,[r0]
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bx lr
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.globl GET32
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GET32:
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ldr r0,[r0]
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bx lr
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.globl dummy
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dummy:
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bx lr
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74
uart01/uart01.c
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74
uart01/uart01.c
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//-------------------------------------------------------------------------
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//-------------------------------------------------------------------------
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extern void PUT32 ( unsigned int, unsigned int );
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extern unsigned int GET32 ( unsigned int );
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extern void dummy ( unsigned int );
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#define GPFSEL1 0x20200004
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#define GPSET0 0x2020001C
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#define GPCLR0 0x20200028
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#define GPPUD 0x20200094
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#define GPPUDCLK0 0x20200098
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#define AUX_ENABLES 0x20215004
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#define AUX_MU_IO_REG 0x20215040
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#define AUX_MU_IER_REG 0x20215044
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#define AUX_MU_IIR_REG 0x20215048
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#define AUX_MU_LCR_REG 0x2021504C
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#define AUX_MU_MCR_REG 0x20215050
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#define AUX_MU_LSR_REG 0x20215054
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#define AUX_MU_MSR_REG 0x20215058
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#define AUX_MU_SCRATCH 0x2021505C
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#define AUX_MU_CNTL_REG 0x20215060
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#define AUX_MU_STAT_REG 0x20215064
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#define AUX_MU_BAUD_REG 0x20215068
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//GPIO14 TXD0 and TXD1
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//GPIO15 RXD0 and RXD1
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//alt function 5 for uart1
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//alt function 0 for uart0
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//((250,000,000/115200)/8)-1 = 270
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int notmain ( void )
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{
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unsigned int ra;
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PUT32(AUX_ENABLES,1);
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PUT32(AUX_MU_IER_REG,0);
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PUT32(AUX_MU_CNTL_REG,0);
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PUT32(AUX_MU_LCR_REG,3);
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PUT32(AUX_MU_MCR_REG,0);
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PUT32(AUX_MU_IER_REG,0);
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PUT32(AUX_MU_IIR_REG,0xC6);
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PUT32(AUX_MU_BAUD_REG,270);
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ra=GET32(GPFSEL1);
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ra&=~(7<<12); //gpio14
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ra|=2<<12; //alt5
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PUT32(GPFSEL1,ra);
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PUT32(GPPUD,0);
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for(ra=0;ra<150;ra++) dummy(ra);
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PUT32(GPPUDCLK0,(1<<14));
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for(ra=0;ra<150;ra++) dummy(ra);
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PUT32(GPPUDCLK0,0);
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PUT32(AUX_MU_CNTL_REG,2);
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ra=0;
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while(1)
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{
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while(1)
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{
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if(GET32(AUX_MU_LSR_REG)&0x20) break;
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}
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PUT32(AUX_MU_IO_REG,0x30+(ra++&7));
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}
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return(0);
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}
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//-------------------------------------------------------------------------
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//-------------------------------------------------------------------------
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